is there a bathroom in the space now or would the contractor be breaking up concrete and running new plumbing?

All other concerns aside, inexperienced DIYers should be pretty careful thinking about cutting large chunks of vertical concrete themselves.  

Polish it up, do some re-hab and raise rents as leases will allow.

Because there is space left for 3 more homes but the concrete slabs aren’t poured yet.

Budgets are guidelines not concrete. architects blow your budget, contractors have great intentions but are like kids you have to watch them Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

I believe (but don't have concrete proof) that them having a commercial lease and running a business in a residential property is reason for me to terminate their lease. 

If it doesn't hold pressure, then they would jack hammer into the concrete slab to fix the pipes.

Your concrete costs for roads and other was probably per market price. 

Know yours, and explain your wishes to the workmen (not wanting the roofing crew to start at 6am in August, but at noon, might be a no-go for the contractor, so always ask about start and end times).If you are going to have concrete poured, understand how to slump it, and do so.And @Jay Hinrichs, do your Mennonite siders ride horse to work (if so any pics).Just my 2 cents.

Grounding rods or structural rebar for concrete