I'm still not able to rent for higher, just same as before considering the down season during winter and changes in market- There were few options as far as where to install, I decided to go with next to kitchen sink- Additional thing I decided to do/pay for is replace the sump pump, as the existing sump pump was too small to handle a 1-bedroom basement per plumber. 

Here there is no such thing as a "Debt to Income" ratio...because your income doesn't matter. 

My thought is a large concrete wall higher than it and the flume as well as additional fence, soil, tree boundary.

If you need to evict a tenant and don't get paid for 6 months and in addition need to pay several thousand to repair the place to rent back out will you be able to handle that?

Study what needs to be done to learn everything you need to know about the rehab process, vetting contractors, managing debt, vetting tenants, taking rent.

The only challenge I see with your request with that we have to offer is that you're looking for a hybrid equity/debt partner (like mezzanine financing) where lenders like us only provide debt financing.

The longer they stay high, the more investors who thought it was a good idea to buy 3% cap buildings on cheap debt a few years ago are going to get bled out.

HELOC gives additional flexibility for a higher interest rate.

The applicant has no verifiable income (he is an artist and woodworker), but has basically zero debt and an excellent credit score (almost 800).

Either with residential or commercial, yes, there are programs that would allow you qualify based on income/debt.