They won't cover anything pre-existing, so if its already leaking, they will deny the coverage. 

My wife and I are retired and working on our existing rentals as opposed to buying new for now.

A lot of options I've been seeing, like HELOC and Home Equity loans, require an LTV of around 85-90%, so I was wondering if there were any creative ways I could still leverage the existing equity in the home?

If you think the prices are too high to buy an existing building in Brooklyn, you won't find the prices for knockdowns any better because they often come with environmental issues, removal snags, and then plans, permitting for new construction is very difficult.

Return on EquityROE = Net Income / Invested & Existing Property Equity.So drawing on your example.

I would highly suggest discussing this with your CPA, especially given you already have an existing business.

His existing business is booming, to someone like that a (what he might regard as, but this isn't actually a quote) "stupid little triplex" is a waste of his time.TLDR: People that are a good fit for DSCR loans don't want them.

If you know what you are doing and doing it at scale, you can actually pay up (within reason) for properties that will help you increase the appraisals on existing properties.

After searching, locating and researching a piece of retirement property, we are considering an offer to the seller's agent (who knows very little about what he is selling).As the buyer's agent is typically compensated by the seller, is it normal to ask for a reduction similar to the 3% that the buyer would pay to the non-existent agent?  

What contingencies exist in case you for some reason cannot finish the project?