Commercial loans are typically shorter terms with a balloon payment at the end of the term and are more strict regarding the cash flow and investor/owner finances/assets. 

Fast forward a few weeks after I move out I receive a security claim letter along with an estimate from some random rental maintenance company that says "unit turnover".

So, you identify an asset and do your homework, make an offer with your pre approval letter from the lender, it gets accepted. 

Diving in on some value add opportunities with a seller carry and a 5-7 year balloon contingent on appraisal. 

However, I recently got an offer letter that will require me to be on site.

Email, phone call, letter?

Are you available on the weekend to send a pre-approval letter if I need to get an urgent offer submitted?

In my opinion, more ethical marketing methods include SEO, postcards/letters (which I do not find disruptive... the line is rather or not the marketing interrupts me. if I am already processing mail I don't mind eyeballing a few wholesaler mailings per day while I'm doing it), building relationships with realtors and others...

Is there a letter format to follow?

If the loan isn't full note interest you wouldn't be paying monthly on the rehab money until its actually drawn, if you never draw the money you won't owe it at the end when you request a payoff letter.