But what I never hear anyone discuss is how the payments on the HELOC, whether interest only or principal and interest,  factor the overall cashflow and return?

Vacancy and all expenses (except principal and interest) are on the other side of the ledger.

I would highly recommend that yousave this documentation until the loan matures, and you receive a return of principal."

Also the principal of this and pain somebody was trying to rip us off as difficult.

Both FNMA and FHLMC permit this, under the following circumstances: Notes: For all such transfers affecting mortgage loans purchased or securitized by Fannie Mae on or after June 1, 2016, the transferee is not required to occupy the propertya limited liability company (LLC), provided thatthe mortgage loan was purchased or securitized by Fannie Mae on or after June 1, 2016, andthe LLC is controlled by the original borrower or the original borrower owns a majority interest in the LLC, and if the transfer results in a permitted change of occupancy type to an investment property, such change does not violate the security instrument (for example, the 12 month occupancy requirement for a principal residence).The servicer must notify the borrower that a property transferred to an LLC must be transferred back to a natural person prior to any subsequent refinance application in order to meet Fannie Mae’s Selling Guide underwriting requirements.Citation: D1-4.1-02: Allowable Exemptions Due to the Type of Transfer (04/13/2022)Now, you will still have the Note and reporting in your name individually and will still be personally responsible for the mortgage and most likely, the manner of transfer will enable any litigant to pierce the veil of your LLC, but you'll have what you wanted, for whatever reason. 

So for instance, if I have 20% leftover every month, that goes directly to principal. 

I have very little hope on what principal will be paid back if that day ever comes!

But what I never hear anyone discuss is how the payments on the HELOC, whether interest only or principal and interest, factor the overall cashflow and return?

I can see this principal applying more broadly to AP subject you are raising, but also as the STR legal landscape develops (and the end game there seems to be eventually heading towards a more unified policy and even constitutional argument in front of the Supreme Court, in my opinion) - this may apply very readily to a sound legal strategy for STR protection? 

The builder makes monthly interest payments and repays the principal once the property is sold.