I decided to send a polite letter with photos to the tenant (who left shortly after the portable washing machine was discovered) outlining my losses not covered and asking for a small cash settlement from them.I thought they would either pay or discard the letter.

Outline where you want to be in five years.

When I find a buyer, the buyer is actually signing a contract with the wholesaler, and this second contract outlines my commission to be paid by the wholesaler.

If you do not have this outlined in the lease, they could theoretically stay as long as they like.

I have a lender that I work with who's an investor herself and incredible at creating strategies to move forward on your next purchases (she helped us devise our strategy outlined above).

Like outlines/ summaries of past deals, etc.?

It should outline their pet police, what they can charge, and who keeps what. 

Be sure to speak with an attorney and draft an operating agreement outlining everyone's roles and who's entitled to what.1.

@Andrew DayOn Joe Fairless is podcast they have a series called syndication school which pretty much outlines everything needed for syndication.

This helps take the emotion out of situations like the one you are in because everything is clearly outlined.