I like your idea to use other people money on a simple interest term.

This Is a common concern for people doing a 1031 exchange.

You'll see plenty of people posting about the negatives. 

If the new rates are market, where are people going to move their stuff?

Equity partner gives you the money for a portion of the profit and is usually on title.In buy and holds, there are three people to each deal if you include financing.

Not saying you did, but often people love to quote the cashflow but conveniently leave out capex, which can be considerable on a bunch of individual houses. 

Based on what you've provided here, I'm going to assume the partner is a friend or family member- and not to rub salt in a wound, but most people think that makes a contract LESS necessary, which is the total opposite.

Do you guys / gals, see a problem with the renovated units not having the ability to intercom / buzz people in through the front door until a new system is put in place (which may not happen for years or ever)?

Vacasa and Evolve hire local people to look after clients they get in areas.

People do not value their time, which is your most expensive asset you have.