I would personally do the later, keep the interest rate, and start your rental portfolio.   

It's a highly nuanced industry that isn't very regulated so you will need to know what you can and cannot do legally and then create some personalized guidelines around what you want to fund and what you want your returns to look like.

If you can't keep control of your personal finances, you are highly unlikely to succeed in real estate investing.

Podcasters that does house walk throughs will sometimes say, "if this Floorplan isn't available in your city/state"  blah blah blah.

If you are moving it from a personal name to an LLC there is an exemption form for taxes you also have to fill out and file along with transferring the deed.

I'm working on helping some clients/friends of mine get their condo rented as a medium term rental, but not getting many hits on it, only one person that never answered me back after multiple calls and texts (stay has to be 30 days or longer).  

For example, I would need a new loan from a bank for the remaining $550,000 after the 4 years or would refinance the house for the $550,000, correct? 

Have you considered house hacking? 

Personally, I find that a bit steep and would probably look for another company.

Check whether the area has any max unrelated person ordinances.