Until you know the factors that surround the poor credit score, you don't have enough information.

I would not require any structural improvements to the slab at this time, but I would recommend the owner maintain the following items in the future:Maintain grading around the foundation of the house per the attached specificationsKeep soil near the foundation walls moist during dry weatherExpect cracking in floor, and seal with flexible sealant when visibleThe proposed maintenance is designed to retain strength of the foundation.

I think you're so right that it depends a lot on factors specific to each investor's comfort level. 

I am seeing more and more of these spread sheets and none of them have leasing fee's therefore the vacancy factor is under funded.unless you have a deal with your management company to lease the units for free. your going to have turn over.. everyone does .. and its not common to have a tenant leave and not have a month of vacancy plus a lease fee.. and of course turn over costs.. although I was happy to see your contingency line most folks don't put that in there..

Worst case scenario factor in the cost to completely redo the conversion, or rip it out and convert back to garages might be cheaper, take that amount off your offer price.

Is the sweetspot to find a middle-tier school district or is it a non-factor?

If you go that route, you'll need a survey anyway so factor that into your costs.

There is another factor at play for me, though.

Trying to come up with guesstimates on what I'm looking at with labor and possible material costs psf for simple and basic designs.

I don't think $30-40k in cap gains will matter much to you tax bill, depending on your w-2 income.Over the last couple years I have been amazed at how little taxes are a factor when I report $70k in gains/yr or less.