Best thing to do is buy a new house to live in and rent out the old residence. That way you get a very low primary residence interest rate.
I think SD rentals make sense if you can get 3.25-ish purchase rates or you are investing cash that otherwise would get getting 2% or less as a safe long term rate.
A mostly-financed rental at 4% seems a bit aggressive. Probably it would work out including appreciation, but you’d likely be cash flow negative at first.
