I'd suggest contacting the county code enforcement office (they issue building permits) and ask about the rules.

I am thinking perhaps lease the land and help the local tenants out with finding the financing, planning, permits and utilities.

@Pasquale Zingarella Ask the Planning Department if they have a Special Permit process or Variance process that you can go through to try and add the 5th unit.

And then the actual fixtures and touches are based on preference, but the bones should get in for about $11-12k after permits and drywall.

We had to rewire & replace ALL of ours to meet code & get the permits signed off.

Permits or Paint? 

And as far as the work he's already done(drywall/floors), since there is no recent permits for plumbing or electrical., is it safe to assume that work will have to be taken out to be inspected?

Reconfigure 2 non-permitted rooms into a large master bedroom.

The previous owner added 2 additional un-permitted units in the basement making a total of seven units.

I'm fairly certain it was just built this way, so I'm going to search for old permits, blueprints, and anything I can find to learn more.