If on pipe, just make sure its wrapped in plastic. 

The PROS of condos IMHO are the maintenance factors are pretty low since you own from the walls in and maybe a small patio area while the HOA's take care of the exterior maintenance, roof, building insurance, water, trash, sewer.

It has original windows, front patio needs pressure washing, and the landscape is simply grass up to the house.

He is also very suspicious... parks very large vans (about 4 to 6 at a time) in front of his property and on his driveway to cover the house, has cameras everywhere, is hanging cloths from his patio cover so no one can see the inside of the house, etc. 

Bought below market value, adding Kitchen and patio

Pre-plastic, it seems like septic tanks can either be concrete or steel.  

Remove all flooring boards and replace with plastic decking for a maintenance free repair? 

If you go to home depot and spend $500 on materials, but don't have the receipt, how would the IRS know you did not purchase a new grill or patio furniture for yourself.

Common Area: set ground rules for living room, patio, parking... be very clear about guests (stayovers), guest consistency before they become a tenant, and pets.

You can get a plastic cover