I think the biggest 2 things are competent and organized. 

The way I see it the two biggest draws to SFH for tenants is not sharing walls and privacy of their own yard.

The biggest holdup, if within Baltimore city, is the"lien sheet" that has to be prepared by the city with a list of city municipal bills.

And investment properties are the biggest area of overlays for large banks.  

@Wade StahleDepreciation is one of the biggest forms of welfare that we landlords enjoy.

It was biggest mistake I've made, not debilitating, but I won't buy them anymore.

Repair damaged interior doorframesRepair cracked drywall Repair minor interior water damagePaint interiorRehab kitchensTear down garage, replace with 1-2 unit structureRemove fence/landscape yard (xeriscape for low maintenance) My biggest question is: after I stop water from getting under the house, how long should I wait until I have foundation work done?

This will eliminate the biggest hit financially and when done by yourself will end up with better quality tenants.

I agree totally with @Tim Swierczek, wholesaling is not illegal even thought the way some people do it may be.One of the biggest things I have found in my studies and research is that you can not sell the Property (the home) you can sell the contract. 

Our biggest deal so far was a 120 unit.