I’ve been offering a $100 referral fee for existing tenants who refer a new tenant to any of my properties.

Don't spend time looking for something that doesn't exist.

The account is "Vacasa"'s, not his.Likewise, if Elon Musk decided to buy Vacasa and tomorrow, I'm pretty sure he would retain the accounts as they are assets of the business he's buying, not any particular person.  

Well, what would be happening is that your buyer would be buying your house subject to the existing note, since you can't legally sell the property without paying off that note or transferring the debt to the new buyer.

Common fees will include a set-up fee, a leasing fee for each turnover or a lease renewal fee, marking up maintenance, retaining late fees, and more.

If you don’t, maybe work with or for an existing company first for awhile?

How will the existing income from the property influence the amount I can borrow? 

Common fees will include a set-up fee, a leasing fee for each turnover or a lease renewal fee, marking up maintenance, retaining late fees, and more.

  - Does he want to retain some owner ship? 

When you start, the company may give you a small existing portfolio, but then you'll have to maintain & grow it to make a decent living.You could also work as a leasing agent at an apartment complex.