ATM, I have a rental condo in Costa Rica, a primary residence in CT, and passive investments in HML and in a real estate syndicate. 

Hello,It's not uncommon for traditional banks to restrict HELOCs to primary residences only, as they generally view them as less risky.

Okay...Finally making the plunge and putting my old primary into a LLC or Trust.

You can't take depreciation deductions on a primary residence.I have a feeling that converting this rental to a primary will also unleash a huge tax bill in the form of depreciation recapture. 

We manage a property that is an STR duplex in the primary home, and an MTR in carriage house (above the garage).

I am considering turning my primary residence into a medium term rental within the next 6-8 months, since it is already furnished.

As an investor, your primary goal is probably to buy at the lowest price (you make your money when you buy at below market value), fix it up, and either hold or sell/flip.The seller might realize they "don't know what they don't know"....in general, investors sometimes come across as "transactional" (they ran the numbers, and just want a yes or no from the seller). 

I have heard time and time again that a primary residence is not considered a good investment if you really look at the numbers.

I know that is not always the case.Selling anything right now to have to buy another primary doesn't appeal given rates now vs. what we have, but to your point we might be able to do more with that cash vs. just leveraging equity & financing.I'll run some numbers and happy to share with more data.

Those loans are meant for owner occupied primary residences.