But, I would encourage you to also think strategically about how to maximize the "hack" part of the house hacking strategy.

So cash on cash returns are easily 50%+ i believe this is what Airbnb strategy used to be before pandemic inflation hit.

I personally don't like this strategy as I am getting more calls from sellers who have been done wrong.

I don't have much to add other than running numbers from a few different standpoints such as, realistic, and very conservative, to what seems like may be a stretch, I like it because you get a range of numbers and if none of them work, it answers a lot of questions, if some work you may have to do more research or be creative in other areas such as financing or strategy.

Your Architect should be able to guide you through the rest of the process of design, permits and construction. 

I've been working my way through different institutions and this seems to be a strategy that isn't generally accepted if the loan is in excess of my DTI. 

I am familiar with the that strategy, but it’s not something we want to do at this stage in our lives.

Designed it specifically for Airbnb - added a lot of amenities to backyard

I think building out a strategy and thinking about what you want to do moving forward is a great starting point because it doesn't seem like you have a shortage of options.From leveraging your existing HELOCs, opening a new one, or fully refinancing your property that is paid off, it feels like the biggest concern I would have for you would be 'paralysis by analysis'. 

Be wary of overly creative write-off strategies, as the IRS isn't easily fooled, risking audits and hefty penalties.