Is there a way I can fully create my own authentic detailed avatar with full customization ability?

[Rolig Loon]

Sure.  If you are a talented 3D modeller and have access to the right software (Blender, Maya, .... ), you can make whatever you like.  Well, within reason.  You have to work with the avaiable bones to rig it.

[Rolig Loon]

Sure.  If you are a talented 3D modeller and have access to the right software (Blender, Maya, .... ), you can make whatever you like.  Well, within reason.  You have to work with the avaiable bones to rig it.

[Lindal Kidd]

You already have that capability, pretty much, with the standard avatar body.  Have you fully explored the Appearance slider options?  Once you have a shape that pleases you, you can either look for and buy a commercial skin, and then further customize that with different makeup tattoos.  Or if you have some mad Photoshop skillz, you can paint your own custom skin.  The free skin templates from Eloh Elliot and others will give you a leg up on the project.

Designing a complete, customizable mesh avatar from the ground up is a really huge undertaking.  You'll need to be skilled in 3D modeling with Blender, Maya, or a similar program; skilled with creating custom UV maps and textures in Photoshop; and skilled in scripting to create the HUD controls you'll want for the customization functions.  You can see from the prices charged by creators like Belleza, Maitreya, and The Mesh Project that these products represent a LOT of time and effort.