First, you gif is fucking amazing,and  I hope most of your questions are answered in the old OOC. 

However. for the sake of well being me.

Blood Immortal: Yes, you can has. Though because of the nature of the power he/she must have "tuning" to manipulate blood that is not his/her own. IE: come into direct contact with.

Nature and Vegetation: The "mixed desert" areas are the more vegetative. The green swathes of land on the map are reconstructed Gaen farms, producing a lot of old world goods that can no longer be grown on Dust. Dunes and flat typically have very little vegetation. But yes, it exists, substantially too.

Pre-fall buildings: There are cities that exist within pre-fall ruins, and some cities that arise out of nothing. Off-hand I believe Forbes, and the one to the very east, Fairbury are "ruined" cities. I think Tas too but I'd have to double check that.

Guns: Relics? Yes, I have no constraints on pre-fall items for acquisition. If you want an anti-tank rifle, well I don't see why I should deny it. Guns are pretty common, shoddy ones at least. Ammo is less common, and more valuable, pre-fall rounds are considered military grade and are shiny, pristine, and worth their weight in gold. Dirty rounds are the most common, and are less effective and reliable, but are the main sources of trade. Trade however, is an entirely "barter" basis, you have to have something the other person wants. In this world, everybody wants ammunition. Dirty rounds are like the bottle caps of fallout, you can sell everything else, but everybody wants them.