Sounds like you're essentially renting to a roommate with a few more bells and whistles than room-shares typically receive. 

If you don't mind, please provide advice on house rules, finding roommates, and payment.

Safe to assume it is different between "couples" and just roommates.

I am asking because I have seen so many military members room rent, then leave the market leaving their roommates behind. 

In addition, they charge each roommate $140 for utilities, maid service etc.

So does a bad credit roommate/co-applicant bring their application down enough to warrant denying them? 

I always had a roommate when we moved in.

Single, roommates, spouse kids, etc.2.  

YIf your unit has multiple bedrooms, rent the other(s) to roommates to increase cashflow.This will teach you a lot about landlording and after 1-2 years, you can buy another and repeat the process.

I have a good roommate that pays on time and just does his own thing.. however a few weeks after he moved in (mid-Feb) I heard his toilet (main toilet) running and found he had hooked it a few links higher so the flap wouldn't seal.