I offered 35k per unit and he countered with 50k per unit.These units rent for $550 per month and they stay 90-100% occupied.Would the magic number per unit be in this case?

Desirable neighborhood with great schools.

But the kids need to get to school, crap the dog has fleas again, I already have a solid job. it can wait. 

In addition, I would shoot for something simple like a 1960s built ranch on a slab crawlspace in a good neighborhood with good schools, and stay away from the owner built homes and/or basements for now.

If you're doing buy and hold, I usually just look for the gross rent multiplier to see what's worth looking at, then run hard numbers and check schools and area after that.

@Bob E. describes the school of thought that I subscribe to. 

This umbrella policy covers me if I hit a school bus on the way home, if someone gets hurt at a rental or even my primary residence.  

None of those people want to move frequently, I think families tend to move more because they become pressed to as kids outgrow certain things in the area (school, sports, friends) or new kids are added to the mix. 

3) Does anyone have any experience with the Allied Real Estate School.

I graduated from Texas Tech in 2011 with a Bachelors in Business Administration and went to work for a mid-major commercial contractor out of school.