Its my personal thought that its usually better to get into your principal residence before buying rental property.

I think to do this I would look at an assumed 2% appreciation though it will probably be more along with estimates for cash flow, potential tax write off, and principal paydown to generate your internal rate of return (IRR).A few things to consider. 

Keep in mind this is a variable rate and 10 year treasuries have shot up in the last couple days, some places already quoting 1/4 pt higher interest rate.A heloc will have a lower payment then if you just refinance the 1st position mortgage and do a cash out loan because the heloc is only interest, whereas the conventional loan would be interest and principal, but would lock you in at a low rate...

Even as a general principal it is pretty useless imho.

Pays for itself, plus additional $30,000 cash stream.Cash stream NPV of $105,000 including Principal/Interest, for 30 years, using 5% IRR= $1,614,000 as of start.Thus $414,000/$120,000= 345% before tax impact.

Maybe I’m overthinking it, but if the average person stays in a house for 7-8 years and they’re not really paying towards principal during this time doesn’t it seem a little concerning?

I assume $1775 covers your principal, interest, taxes, and insurance.

This causes the principal and interest portion of expenses to be pretty similar to when prices were lower while interest rates were a little higher. 

So example you lend out $150K:In 6 months you receive your principal + $9,000Basically $1,500 a monthYour name is on the 1st LienWhen the house sells you get a check from the closing agentThis strategy is great since well done flips are selling really fast.

Of course you need to factor in the principal reduction and the equity as the value increases.