The seller offered financing with 20% down, which I used to buy the place.After starting construction and realizing it was going to cost more than expected, I approached a small local bank that knew the property and would offer the rehab financing. 

Why not use bank debt or alternative lender debt if you don't qualify yet for bank originated debt?

This person did not raise any money, they invested around $600,000 into the offering and because they were one of the larger investors were considered a Co-GP because it was a new sponsor and they needed this persons $.

I personally haven't done this but I have helped clients do it in the past.Hit me up if you're interested!

In addition, you want a separate bank account for the rental property to separate it from your personal accounts.

Yes, a HELOC or bank a line of credit is different than a lump-sum amortizing mortgage (DSCR or otherwise).

Banking industry?

RM (and most other good management software) does double entry accounting, imports bank info, has reconciling functions etc.

Look at it as a piggy bank. 

So I get that "lag" almost every time, plus I deal with our corporate bank... so they always have that lag.