As far as my lender I started with small multi family and had met the woman in charge of residential lending at my bank over the years at various local functions.

Fees should be clearly stated in writing, easy to understand, and justifiable.

I just sold my business and in looking for ways to offset capital gains taxes stumbled across a strategy in which a STR can write off all depreciation in year one via a cost segregation analysis, thereby reducing taxable income greatly for a specific year.

In such cases, the property should ideally function as a flip, benefiting from either market appreciation or improvements ("forced appreciation") to maximize its value. 

You could write a simple statement and have all parties sign and date:"Landlord and Tenant agree to extend this lease with a new termination date of June 30, 2025."

The limit on the line will mostly be a function of the CLTV on the property, your DTI, and the lender's risk appetite.

I can’t even seem to write a deal with inspection contingencies at this point so… Personally, I would never take that amount from a relative to “invest for them.”

I would strongly recommend creating one to ensure everything is neatly organized and you don't get flagged by accidently writing off personal expenses. 

I was hoping to get some clarity on the rent collection functionality of the stessa/rentredi platform, versus hiring a property management company.

I also found a small local community credit union who will write first position HELOCs.