we had a tree fall in our backyard of our rental and caused some multiple issues/ roof damage, railing and stairs,  inside the ceiling that got hit may need replacing and some of the floor.My question is should we use one GC to fix this all or segregate some of the job for vendors we like.  

Ceiling to floor rehab, new furnace, new windows, added central a/c.

I know there are leaks as there is a tarp covering the entire roof, there are plenty of stains on the ceilings, and multiple places where the ceiling is missing altogether. 

I always use semi-gloss.. except on ceilings.

However, I will never invest there again...Lot's of horror stories of cats pissing on the ceiling, dogs crapping on the walls, tenants being arrested for sex trafficking...the list goes on.

., painting, kitchen, bathrooms, vinyl flooring, remove popcorn ceiling, update fans, etc.)?

Occasionally but pretty rare you will read agents say “legal non conforming” which could be a legal basement/attic with only one exit or low ceilings that was legalized due to grandfathering, making an adu etc. 

It has rather high ceilings and I think could make quite a nice unit.

I'm not sure I could get a building permit to convert this room into a bedroom.There was only one light switch in the basement located at the bottom of the stairs and it operated both basement ceiling fixtures.

I didn't want to spend a ton sound proofing the basement ceiling so instead I went with a cheaper route where I put down felt padding with a rug on top that covered the entire living space that was over my area.