But things are different now, the interest rates are high.

Income - student debt - mortgage payment - monthly expenses = monthly savings If you're going to go down this route, I highly recommend that you house-hack your first deal.

Which shows you the downside of today’s high rates.

Vibration can be caused by loose pipes banging on the studs or it could be from high water pressure.

As far as it predicting high on revenue, that's obviously the biggest risk and I'd be concerned about that as well when getting into a new market as a short term rental investor. 

Trying to nail in a location that will have high volume of renters.

Great time to expand values are high, rates are going to start to fall again in the next 60-90 days.

I would highly recommend working with a broker that really understands the nuances of this style of loan as each lender has different credit requirements, leverages, and ownership requirements. 

For rentals, aA better thing would be to look at population and job growth in the market.

The second property will be purchased with a mortgage (you can determine how high or low the leverage will be by adjusting the proceeds you use or the price point of the 2nd replacement).You are adding some measured debt at a level that your dad can be comfortable with.