We have an opportunity coming up from a family member who is willing to sell us my childhood home for what they got it for (240k) and the comps in that neighborhood are 600k+.

Considering opportunity cost of not affording more rentals vs paying much more in interest.

Sale your current house.  

The key is that in order to completely defer all tax you must purchase at least as much as your net sale. 

This defers capital gains and depreciation recapture taxes on the sale of your fourplex.After converting it into your primary residence, you may qualify for the primary residence capital gains exclusion ($250K single/$500K married), but only for appreciation after the conversion; gains from the rental period remain taxable.

@Kaaren Hall after seeing your post i called them right away, their fees are extremely high for an HSA that for the most part most people don't have a lot of money in.I max my HSA every year, but if you have a self only plan you can only put about 4k /yr  and if you have some medical bills it's less.they are also very restrictive on taking money out, and no CC to pay the doctor. prior to speaking with them I was extremely excited to see this opportunity you suggested,  but after my conversation I'm no longer...I will look for other options now that I see there may be some, so thanks so much for bringing it up.

That just adds a level of complexity to everything.I think there is so much opportunity in the US, that why would you try to complicate everything x10, but investing in someplace like Spain. 

@Adam Luepke Yes, there are plenty of more affordable rental opportunities in MO.

hihi :) Thanks for your thoughts Jaycee, Not sure I would call it a cash cow but I did think it was providing a opportunity.

It's been a few years, but I had the opportunity to serve on a panel or two at IMN Conferences with Jorge and he's top notch.