So a project's capital requirement goes deeper than the down payment. 

Now take that and add the new inspection requirements and higher commercial property taxes. 

Most of those claims to pay if not closed on time have loopholes/tight requirements and more often than not we have seen the fall-out.This is a lot I know haha but hope this gives some context.

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

The BRRRR method requires careful planning, thorough research, and sound financial judgment.

Or other regulatory requirements?

Some require complete disclosure but some do not.

I'm in the position to apply(depending on lender DTI requirement) for conventional financing through the builder at <6% interest rate in this current market.

If it’s a safety issue, I’ll of course make sure the premises are as safe as they were before any required maintenance was done, but she is now suggesting that if I don’t reimburse her for those specific anchors, I am violating fair housing laws for familial status and/or tenants rights regarding not incurring costs for required repairs.

The main reason we go 50% LTV rather than 60% is at 50% the bank does not require personal guarantees