This sounds risky, are you being compensated by additional rent and have you checked with your insurance to ensure you are covered. 

Additionally, I was not making enough from my corporate job to support any kind of significant mortgage payment.

You divide that $20k by .075 and you get a boost of $260k to the valuation.Allowing you to take the property back to the bank, get a new loan with $208k of additional debt on the property, pay yourself back that investment and now you have enough cash to buy a $1M deal and use that strategy over and over while scaling exponentially.

Given your experience with RV parks and MHPs, you already have a strong foundation for managing mixed-income streams, which will be valuable here. 

This is due to bonus depreciation which allows taxpayers to deduct 40% of qualifying property costs in the first year, in addition to regular depreciation for new construction and improvement.

Additionally, I know the Waivo product for STR covers intentional and accidental damages.

Additionally, while rates aren't historically bad right now, they are higher than 4-5 years ago, and they will be even higher for you as an investor than they were as an owner occupant, which is what you were when you bought originally.I get that you are anxious to add to your portfolio, but that could be achieved without touching your first golden goose.Sometimes on BP, the push is to leverage every last spare penny, but that can be a risky game as the markets shift. 

Sounds like you put in a ton of work to maximize the value, and that basement addition was a smart move.I noticed you mentioned the NYC luxury tax and some of the rental pricing challenges—have you considered expanding your portfolio in markets where you don’t have to deal with those kinds of headaches?

In our market it is important to make sure they are a licensed broker, carry adequate GL and worker's comp (and name you as additional insured).  

Additionally, confirm the transfer won’t lead to property reassessment, which could increase taxes.