[How do SLUV a new topology mesh model?]

So you're far from "new" creator, sorry for assuming things. Maybe I have one more suggestion though. What if you edit head topology in Blender, instead of recreating it from scratch? Most polygon editing tools, like knife,  subdivide or dissolve edges, preserve UV layout when used. And the original head's topology isnt that terrible honestly, you'll just have to dissolve diagonal edges in case it was triangulated on import

https://gyazo.com/bb27c1ed0ad00e2ce0a889a38287a54e

Then you could put it into Zbrush with UVs intact and sculpt .

[How do SLUV a new topology mesh model?]

There is no easy way to do this. Export the UV layout of the standard head, use it as reference image, and unwrap your head manually to match it.

Also take note that even if you manage to do this, it will be pretty much useless because of few reasons. First, the skin products on SL wont be compatible with this head anyway. SL skins only work with system heads and bodies. The creators that make mesh body parts on SL are forced to paint their own skin textures.

The second, Second Life cannot import shape keys/morph animations. So animating the head will be a tremendous task, especially for new creator, as it requires lots of programming and complex, cumbersome workarounds. Like, exporting the copy of your head for each facial expressions, then writing a script to switch their visibility on demand.

[Can I get some help on small custom mesh avatars]

As far as I know, small avatars in SL should be made of two components. First, visual mesh (on import, check only Skin Weights) and second - the deformer (a dummy mesh hidden inside the body, weighted to one of the resized skeleton's bones, on import select both Skin Weights and Joint Positions). For some reason, joint positions never work correctly on the visual mesh. 

[Zbrush Core]

ZB Core doesn't support texture maps. This severely limits its use for  realtime 3d content (game/virtual world models) creation. Only people I see it will be good for are 3d printing enthusiasts. Otherwise, it will require too many extra software to work with, making it not worthy investment IMO

[Animation- worthy SL skeleton for 3ds Max?]

Yeah, using the XML skeleton definition as reference for rotations is a good idea. I'll check it out. Thanks.

 

[Animation- worthy SL skeleton for 3ds Max?]

I do not plan to use avastar in the nearest future. Especially considering that everything except animation is possible to make with Blender native tools.

The Blender bones system handles bone rotations in a different way than most of 3d software. I know how to rebuild Blender armature  to make it properly represent original bone rotations (did it for other virtual worlds), but to do that, I need an original SL skeleton. I'll check  the  SL skeleton pack once more. Though there is none in 3ds Max format, and I'm not sure if the ones that come in *.fbx and *.dae format do have correct rotations. Since the skeletons from official pack were released with the sole purpose of making mesh clothing, not animations. Rotations arent important for exporting weighted meshes, only bone names and hierarchy.

[Help with exporting a rig to SL]

From what I was able to piece together from my tests, first, your mesh must have vertex groups for all 26 mBones, even if some bones arent really used. Otherwise,  the SL importer will fail to recognise skin weights on the mesh. The thing she does at 1.20 (Parent - Armature Deform with Empty groups) does exactly that, creates an empty group for each bone. Do it before you start to paint weights. Other thing to note is the importer parameters (6.12).  You absolutely should check "Include Skin weights" in Upload Options tab. And she forgot to specify object type (This model represents... dialogue). Choose Avatar Attachment for clothing items (the Avatar Shape should be reserved for avatar resizers, the rest of the object types do not support skin weights).

[Animation- worthy SL skeleton for 3ds Max?]

Does it exist? I'm wondering since there isnt any for Blender. Avatar bases available for free have wrong rotations on bones and only good for weighting clothes.

[Rigged mesh problem - Mesh gets smaller when rotated???]

I'm implying that the mesh is weighted uniformly between 2 bones, so it "collapses". While for correct behavior, the hand part of the glove should have only hand bone influencing it.

If you're still confused, I'd advice to learn Blender's native weight paint tools, and the meaning of vertex groups. Tools like Bone Heat and automated weighting provided by Avastar are  "black box" and  do not help understanding the program IMHO.

[Rigged mesh problem - Mesh gets smaller when rotated???]

Looks exactly like a weight paint issue. Not sure why you're so opposed to that idea.

Here is how it looks when the mesh is weighted 0.5/0.5 between hand and wrist:

https://gyazo.com/ad67005a95ce9389955e3fe18f3d99e3

 

and 

https://gyazo.com/7031b617e5fc051b22de2fe5d89a8bc9

 

The same effect will be if they both have 1.0/1.0, Blender will "normalize" that for you. So check if your glove is weighted to the wrist as well. Or to any other unwanted bones

[Texture not showing up in Blender]

Not sure whats wrong. Check this: 

 about 1.18

[Texture not showing up in Blender]

To view Material texture, you'll need to enable GLSL shading mode 

https://gyazo.com/9bf880668bb82d9538e843f3097afa27 

and switch your viewport drawing method to Textured 

https://gyazo.com/fe9b7f0802a3ebda2c783d487ee1c706

If you have texture applied to the faces in UV editor, you'll need only step 2, or enable Textured Solid in Solid drawing mode. 

 

[So I got into making resized avatars...]

Hovering height is set so avatar stands on ground firmly. I cant set hover height for sitting separately. Thats why I looked for scripted solution. Since sitting action can be detected by script, and make script to do stuff according to it. The question is what to make it to do. So far I havent found the way to script z offset.

And no, I'm not using animation overrider here. Just  resizer with custom joint positions.Maybe a good idea though. If we can add custom sitting animations, I can raise avatar root position that way. I'll look into it as well.

[So I got into making resized avatars...]

https://gyazo.com/8b595226fddb320865afe4d8566b4c17

... and the problem emerged. Taking a seat causes it to bury into the ground:

https://gyazo.com/13b87f8fda0e3f158c6cc54840ac2d50

Yeah this is common problem, but asking anyway, maybe the solution is found over the years. I can detect when the avatar is sitting from script, but not much more. Neither edit its Z-position directly or somehow use llSitTarget to tweak it (since latter requires sitting on specific prim). 

[Mesh Clothing Clipping Threw]

 Also if you need better preview of the deformation, create a test animation for your Blender skeleton. Just some random poses. This way you wont need to export every time just to check weighting

[Mesh Clothing Clipping Threw]

yeah thats what arton Rotaru and I tried to tell. Simplest solution. As long as no one will be specially peeping under it, it should be fine.

[Mesh Clothing Clipping Threw]

You can try as SassyRomano said. Retopologising. Though it is easier to weight clothes that you made poly by poly, while being mindful of correct edge placement from the start.

Deleting the occluded polygons is a good band-aid fix too

[Mesh Clothing Clipping Threw]

When I make such meshes, I usually build the "proxy" mesh with even network of quads
https://gyazo.com/b5c231153815cc95c08f715e43015b23, then weight it manually. So later I can use weight transfer tool to copy its weights to any clothing layers I have. Another thing to remember is to have similar topology on all the layers (similar number of edge loops) https://gyazo.com/388532542716295cd93a200d3a80e03f. In this case one can expect all the layers to bend correctly. But since you're using Marvellous Designer for making meshes, you're not having any control on topology. So interpenetration is almost guaranteed.

[Odd Unwrap of "Spring" - Hints appreciated]

Confusing wording by me, but yes, I meant what you did now. 

Well, I suppose Blender unwrap solver isnt perfect and still can be confused by complex surfaces

[Odd Unwrap of "Spring" - Hints appreciated]

you can straighten the borders of the single quad (by scaling to zero, S - X - 0 and S - Y - 0), select this quad in UV view, and then go to 3d view - Mesh - UV unwrap - Follow Active Quads.  It will straighten everything if the mesh has uniform topology

[Anime Mesh Avatar]

The technique is very simple and reliable: make a copy of your mesh, inflate it along the normals a tiny bit (Push modifier in Max, Srink-Fatten in Blender), invert its normals and combine with the original mesh. The front faces ot the new mesh will be invisible, and a narrow margin determined by offset of Push/Fatten will act as outline. This will double the amount of polygons though.

[Blender Joining (CTRL-J) Causes Problems]

Normal flipping usually occurs if attached object was mirrored (negative transform) Before joining, apply the mirrored copy's scale and rotation, and if normals become reversed, flip them the correct way.

 

[Mesh clothes' physics shape]

Good to know then. It would make sense if Avatar shape used physics when worn, but if 

it is not the case, it means less headache.

 

[Mesh clothes' physics shape]

Thanks for clearing that. One more question, if you won't mind: does uploading as "avatar shape" and "attachment" make difference? Will the object in both cases be phantom?

[Mesh clothes' physics shape]

I wonder up to what extent the physics shape is used by clothing? Is it taken to account when the clothing item is worn, or only while the item is rezzed to the ground? Can I, for example, use a simple box for physics shape, instead of low res version of the mesh?