We are saving around 50%+ of our income on a yearly basis, while also putting away for retirement and we would both like to get out from under the mortgage on our primary residence sooner rather than later.After plugging in some of our numbers to a spreadsheet to simulate a first lien HELOC it seems to indicate that we would be able to payoff our primary residence in ~10 years while also paying significantly less in interest from a conventional mortgage.

There is plenty of equity in the 9U, the 4U, and my primary residence.

You rent to these people knwing their past history and something bad happens, and you will be on the hotseat.As I understood your first post, you are a fun-seeker, looking to move towards your goal....adding significant risk like this may/may not help you move faster, but the downside is the risk.Chasing the almighty dollar as a primary course of action is usually a not-smart move....take it easy, take it slow and chase fun. 

With this said, all went through fine I was contacted by the FHA representative about three months of owning the deal and I had to write a letter explaining why I had not occupied the premises.

Once we hit that goal, we sold the property with the most equity to buy her dream primary home.

Buy a new primary home and rent out your existing home.

We've had an Airbnb out of our primary residence basement for 2.5 years.

They require enough space in the primary driveway for the ADU and primary home.  

What is your primary investment strategy? 

While there are some nuances here, the basic premise is that an Admitted Carrier submits their forms and rates to the state for approval.