To keep tenants on track you should insure they are all on M2M leases when their present lease is up for renewal. 

So check foundation, keep a close eye on it for a little bit, take measurements of the crack and anything you can in the foundation to track changes.

Mortgage, utilities, maintenance will match or exceed the purchase price and out strip normal appreciation which historically track annual cost of living increases. 

Tracking all income and expenses on everything you are responsible for and review them regularly so you can hopefully reduce expenses and increase income.By the way, I'm now 60 years old and quite opinionated.  

Typically those lenders want to see a successful track record (even just 1 or 2) before they get on board.Also, a bank usually won't give a conventional mortgage if you're also borrowing DP and construction costs.

We track water use for our well and a single leaking sink faucet doubled the use of 7 tenants.

Since you already know how to track down absentee owners, you would get a better fee. 

I just purchased Excel so I can have a more sophisticated and professional way to keep track of my rents received and profit/loss etc.

Should I keep one spreadsheet for tracking prospective properties and recording the results of my due diligence, and another for tracking sales results post-deal? 

But a few key pieces of your story are missing. 1) what are you doing now and how does it relate to HGTV/flipping2) what were you making a year before you jumped into flipping homes and how much are you making now 3) what was your life needing to be saved from4) your wife, how is she involved in your business5) what did you bring to the table that your friend was willing to cut you in to his successful business6) you said a career job and benefits out of college might not have let you get on this track but you were a top producer working in sales for several years; surely they also gave you benefits by then.