Also, the current system I use for LTR won’t be sustainable as we continue to purchase.  

You've probably heard of big Landlords losing property, but only because they were flagrantly violating Fair Housing, running a slum, or otherwise violating the law in an egregious manner.

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

Therefore your focus should be spent understanding how to operate your business in a manner that avoids conflict and liability exposure because that's the best line of defense.

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

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).

Before we get started we would like to come up solid written business plan that is organized in a clear and concise manner.

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.