There is no grade on their roof to guide water to my drain/gutter...just a break in the flashing that divides the two roofs.

If you're hitting up Cleveland I'd start by reading The Ultimate Guide to Grading Cleveland Neighborhoods. 

All investor-grade assets. 

You could probably get away with doing a 4' high wall and grading the rest.

So the question I've been struggling with is should we build a super basic rental home (builder grade or less) or build a home with features to make it sell easily?

The duplex likely has rental grade finishes and therefore, could be slightly less than a SFR.

@Lamont Marable check your local building and fire codes...putting living space below grade carries a lot of life-safety requirements and needs to be permitted...worst case...if there is a fire and tenants cannot escape...and you knowingly put living space below grade without the required safeguards in place...RE investing career over...Just do it right if you venture down that path...hiring an architect is always the best approach to something like thisBest of luck

I was in 5th grade when we lost the mobile home.

The expensive part is most cities require that the vertical walls need to be jackhammered to 2 feet below grade (ground level) and you cannot through the chunks of wall into the pool.

There are realtors/investors here more seasoned than me who could probably give some others from experience, but here's a stab at your question. 1.) land grading around the house.