After the seller financing is paid off in 4 more years, this property should create a 15% cash on cash return: airbnb.com/h/majesticlodgecostaricaWe are currently also expanding our beach house, which is already a six bedroom home that can sleep up to 28 people.

Yes, there is a chance the payment could be rejected for non-sufficient funds on the 19th, but I'm managing 400 rentals and it's pretty rare and the Tenants make good on it 99.9% of the time.

I have found that the best answer for YOU is what will allow you to sleep well on your pillow at night without thinking too much about it.

Your primary insurance policy with $300,000 in liability coverage should be sufficient in 99.999% of all lawsuits.5.

Being that you already have property management experience and feel confident in your ability to manage a single-family or multifamily property, it really comes down to your financial position.If you have a good amount of cash available to put a down payment towards the purchase of a property and maintain sufficient cash reserves (or if you have a partner you can work with who does), then there's nothing wrong starting off with a multifamily property. 

So I can sleep at night knowing I wasn’t trying to take advantage of them.

And my feeling is for MOST people Solo 401k is sufficient to meet their needs, and an actuary creating a custom plan is “overkill”.  

But paying down a mortgage does let you sleep better at night too.

I think if you can write a solid letter of explanation stating that you are going to commute to Colorado from Washington for 4-5 months out of the year for your job (and why), that should be sufficient enough to run this as a primary residence. 

I hope you have verified that there will be sufficient equity and that you'll be able to qualify (either DSCR or Conv) for a takeout loan or cashout refi for the hard money.