We have >$2m in debt spread across the investment properties and our primary residence.

In Denver where I invest it's actually a PLUS to not have the other unit considered separate because permits are only allowed for STR if you're renting out your primary residence and I know many folks who put a locking door on part of their home and have a separate external entrance to that part of the house, and rent it out as an AirBNB without it being considered an additional unit by the city.

Are there additional primary residence requirements such as homeowners exemption required, or anyone know if this is coming down the line?

However, I am the primary owner.Current Situation: My aunt’s daughter (my cousin) lives in the house rent-free.

From my observation/experience, Berryessa and Piedmont Hills areas are more family-oriented, so the demand there is generally for primary residences, renters, or travelers visiting families.

Do you have over $200k in equity in your primary home?

When we look at the 10yr treasury, for years we bounced around 2'ish %.   

You can buy a single family home, live in it for a year, then rent it out afterwards, and that would effectively be an investment property after you moved out, but you also got the more beneficial terms of it being a primary residence loan.You could buy a single family home and rent out bedrooms while you are living there, and that would effectively be an investment property, but again, you have the more beneficial terms of a primary residence loan.I wouldn't get caught up so much on if a property you buy is an investment immediately so much as I would focus on what your goals are and how each purchase would be step towards your goals, whether that is house hacking or just buying investment properties you don't live in. 

I tend to pay back within 6 months, so my score bounces up pretty close to the original score after the final payment is made.

If my primary residence has $500k HELOC, could I use it to purchase a 2nd primary residence and rent out the first one?