I know it is a very competitive market as well, but if you want to build something sustainable you will need:1) Sources to send you options. 

Investment also spiked in Class A Short-Term Rentals (STR) and investors started paying higher and higher prices based upon anticipated STR rental rates, that exceeded sustainability based upon Long-Term Rental rates (LTR).

Your approach of starting small, leveraging cash flow and profits from other properties, and taking advantage of opportunities like buying below market value is a smart and sustainable strategy.

Ideally, I'm seeking an investment property that is self-sustaining and generates consistent long-term income.

Structuring your financing properly allows for sustainable growth while mitigating risks.

Investment also spiked in Class A Short-Term Rentals (STR) and investors started paying higher and higher prices based upon anticipated STR rental rates, that exceeded sustainability based upon Long-Term Rental rates (LTR).

Any tips for finding that sweet spot between profitability and sustainability?

What would you say is the starting capital needed to sustainably invest in real estate?

how sustainable is this model?

Personally, I am avoiding those markets for now just for a sustainability and environmental outlook, but I would overestimate for insurance premiums, almost 2x what you think just so you have a buffer.