In theory you could demo the concrete patios and install wood decks, but not sure if anyone would go for that… 

It makes for some sweet demos, but it's not much better for learning than a search engine.

Daria:You should absolutely not tackle any demo or renovation personally unless you are comfortable with performing the work, the point I was trying to make was as far as asbestos abatements go, removing portland cement siding is hard over of the less risky end of things.My intent was to share my experience so that the next time you encounter portland cement siding (w/ asbestos), you will know that it can be encapsulated safely or removed relatively easily and inexpensively.

@Antonio Chelala  I found asking for demos and talking to the sales from those companies directly to be effective. 

Suppose those units that are tears downs have an ARV that is lower than what it would take to demo and rebuild?

@Ned Carey is your Baltimore expert.It is different in different parts of the country...in my area water bills go with the person who turned it on....ie previous owner or tenant.However I think in/around your area, government gets smart and goes after the current owner, or you have to have it paid off before you can get it back on.Not all liens are wiped out in tax sales....typically government liens like demo/mowing/taxes don't get wiped out.

He'll know after the first day of demo if my approach is too expensive.

He provides a demo you can try out.

Would a GC even go inside the place with a significant mold issue, or do you have to hire a mold specialist to do that demo so you're sure they have proper protection for their crew and tent off the area to limit spore dispersal? 

I see investors remodeling for the demos that are already there instead of the higher paying who want to move there.