It seems like every city, county, and state has its own rules, permits, and tax requirements for short-term rentals, and I’m finding it overwhelming to navigate all the different layers of compliance.For example, some places require business licenses, transient occupancy tax permits, or even special zoning approvals.

This method is a little riskier and requires more work from the Property Manager. 

I've already contacted the county planner and was told I'm not able to convert this garage to an ADU because of setback requirements.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

LTR tenants are required to have the home professionally cleaned. 

you can get financing witha  LLC but the lender will require a personal guarantee on the loan.

What type of transaction fees should I be looking to pay and is there a down payment required?

I just learned this has now become a voluntary requirement for the time being as there is a court order to stop this reporting.

Windows would be my next check-point (less than R1) and then wall insulation: I would not be surprised if they have no insulation inside, but you can do blow-in, which only requires a small hole.A home looses heat in two ways: heat conduction (which you can slow down with insulation) and drafts, which in old houses is usually the biggest culprit.

Most lenders typically require a 30% downpayment.