I'm getting ready to tackle my very first BRRRR and I wanted to see if the community could share some common mistakes to avoid?

Common fees will include a set-up fee, a leasing fee for each turnover or a lease renewal fee, marking up maintenance, retaining late fees, and more.

Is 20 year ground contact lumber common?

Each of the scenarios, I anticipate can be a headache for bookkeeping and have pros and cons. 

Agree to a lease that allows you to cancel the lease with minimal notice the moment anything goes wrong.Ask for references and contact themSide note: make sure you can actually get insurance to cover you under this scenario before agreeing to it.

Even if I put all of my $120k down, and assume that I can collect $800 per room (in worst case scenario), I am still in negative cash flow.

1) have a building inspector come out and see if your shower answer is legal, proper, and common. 2) if so, and there’s no other reasonable cure lower their rent for the inconvenience, offer to let them out of the lease?

A common serious issue would be no heat in winter time.

Your story of "bad" financials that banks laugh at is all too common.

So, that suing after the return of the deposit is possible although probably not common.