Separate the work into 3 separate categories: 1) Those that are specifically related to the future STR usage, 2) Those that benefit you while living in the house and have zero bearing on the future STR, 3) those that benefit both you and the future STR....assign a percentage to the usage.Be specific and complete.

Good luck with all your future REI ventures!

Both properties have a substantial amount of equity that’s essentially sitting idle.Would it be a good idea to tap into this equity (through a HELOC, cash-out refinance, etc.) to fund future fix-and-flip projects or purchase additional rental properties?

Pay your vehicle loan, credit cards, etc because in 12 months all of the accounts you pay out of a business checking account will be omitted from your DTI in the future. 

My hope is I can gain their trust as a property manager and eventually be the one they turn to to sell later on or refer for business in the future.

@Daniel Medellin Regarding your question, it would depend on the lender or bank you're working with if you want to go that route in the future. 

@Chloe SalcedoStarting your real estate journey at 23 is an incredible opportunity to build a strong foundation for your future.

There are several ways to find out which cities/areas cash flow and get a good idea of things like market rents, ARV potential, and future appreciation.

You may want to find out what you can legally add to a future lease.

The bottom line is that past performance is no indication of future returns.