I began by trying to do the math on my primary residence, but my calculated PI is ~$170 higher than my actual PI.

Do the math.

Hobbyists buy a place do the simple math and after a couple years sell it to an investor (for less than they paid) because (I hate rentals!

Figure out your goals first, realize that OOS investing will take a bit more leg work to connect with people in the area, do your homework to learn the market, and be comfortable with overseeing or managing from a far.

The math seems to work, but I just fear that I will sign it, and not get a buyer, since I've never done it before.

For simple math, if my investor gave me $100k and I paid him 8% that's $8k.

If it really is a deal and you have really done your homework it will sell.

Good idea but make sure the math works before you start quit deeding.

Do your math and research.

Do the math, and you'll see that partnering is a lower-risk, higher-reward solution than high-priced hard-money (at least in my experience and the numbers I see).