[While I am not using my Premium account tier, does it accumulate in my account, or is it lost?]

It doesn't roll over. You get the first 512 sq. meters of tier free with your premium account. But, if you put it in a group you get 10% extra tier. Just be sure you understand the group dynamics. Groups can cost money if you are liable for their costs. If it's your group you don't have to worry about that though

[Abandoned land was raised before abandoned. It's blocking my view, what can I do?]

I own a lot across the street from an abandoned lot. It's a thin parcel that was raised before it was abandoned. I'd like it to be lowered to match surounding lands, that would unblock my view of the water.