I know little about owner financing, and to be honest, if I take on a 300k house payment (or even 250k for that matter), I would struggle to make the payment if I had a prolonged vacancy due to my current W2 income. 

Interest income is interest income, unless you decided to roll some of the current cash into a self directed IRA at which point your interest income would be deferred for a later time and allow your funds to grow tax free.

Renovated in 2023, annual gross rents $144k + utilities.

With two rentals, you might consider QuickBooks Online Plus, which allows you to track income and expenses by class codes (ideal for separating each property’s income & expenses to assess profitability by property).

Is your Adjusted Gross Income over $150k where you can't reduce your income with rental losses?

This will vary based on region but in general 2 – 5 points, 9% - 16% APR (meaning this is the annual rate so divide it by 12 to get the monthly interest amount), and documents fees can be from $600 – $1,900.

New-home sales hit a seasonally adjusted annual rate of 698,000.

I use apartments.com, so the money didn't end up in my account until 1/6/25.Is this considered income for 2024 or 2025? 

My wife and I have business income and our accountant can divide the income according to what would be the best for reducing tax liability.  

The trick is getting from 0 too that $1m+ equity that returns 10%+ net annual in cash-flow.