So far mostly people are telling me I'm probably stuck until their lease is over. meanwhile I also need to pay down my debt and improve credit score. 

Typically Conventional will end 42% of DTI and FHA can get up to 51% DTI (and based on your credit score I think you should stretch to that 51%) Just a few things to start thinking about as you are working through the process. 

During the renovation, I faced several challenges due to the home’s age and hidden damages, including ruptured plumbing, termite infestation, rotted wood, and lack of insulation.

Why set a 600 credit score if it's negotiable?

So act quickly, do as the others are saying and screen him according to your standard criteria. credit, references, eviction history, etc.

I would at least recommend you have them shop a policy for you.One thing we did note is that with hail damage to roofs, they seem to be decreasing coverage/increasing deductibles on that if ever needed.

The credit unions tend to have lower fees and offer solid business products.

That way, you might preserve some of your monthly profit while still knocking out that line of credit.

They focus on safety issues, such as wood rot, water damage, and structural integrity of balconies and decks.

I have already been fully qualified for both the line of credit and DSCR.