I have spent the last 2 years attacking my student debt which has allowed me to become acclimated a frugal lifestyle.

I am fortunate in that I break even on expenses and debt coverage with only 3 units occupied - this 4th rent is essentially my monthly cash flow.Also, and related, am I being impatient with my property manager?

You should hold a minimum of 4 months - 6 months month debt servicing cash on hand.

I was especially surprised to see that non-borrower household members could be included in the new debt to income calculation!!!

It all depends on what your debt to income ratio is.  

Credit score is currently about 710 because I have 90k in ccard debt.  

Given that I don't have much to begin with, plus my debts, it's a bit hard to let go of any significant amount.

Escrow should credit you, the buyer, from the seller's settlement funds at close of escrow.Make sure you get all collected fees, not just the security. 

Be careful about the other borrowing mentioned above - too much of that relative to your income will hurt your Debt to Income ratio and either prevent you qualifying for a mortgage or push your rate up.You also need to know what a good deal looks like and how to run sales and rental comps (or have a realtor who will do it for you - you want them to value the property from an investor's perspective - ie: most likely appraisal value after repairs).

They take on debt based on the job that pays high money will always be around.