Need to run electrical, insulation, sheet rock, closets and 2 windows.Thinking $4-$6000 material.Electrician will be your most cost. ( labor that is ).Everything else is pretty simple .Are you thinking of pulling permits?

I have seen people online switching to insulated concrete forms (ICFs) for the foundation and walls instead of traditional framing to save on the costs of wood.

Talk to the third floor tenants again or look at solutions like ceiling insulation and carpet to help.

It needs drywall/insulation, flooring, a complete kitchen, and new windows.

Will depend on your zone as well as other things like insulation. 

It has to do with the amount and type liablility insulation that an LLC offers v. an LLP. 

Additionally you are going to have to think about insulation (architect can give guidance on this) -- a converted attic will get extremely hot in the summer.It then comes down to costs of construction versus rents.

Repaired and painted fencing; repainted and repaired exterior where needed; lawn care; interior paint in all bedrooms and bathrooms; small repairs within interior; added hardware to kitchen cabinets; removed insulation from crawlspace and added vapor barrier; flashing and siding repairs; removed junk from yard and exterior building...

Example, just because a garage is finished with insulation, drywall, flooring, hvac, and high-end finishes, does not change the fact that it is legally a garage (by building standards).

Get several and put them in multiple rooms to see the differential in rooms at the end of a duct run or that have more windows/less insulation.