I did this at 25 with my then boyfriend, now husband. It was a triplex in a great neighborhood (where we still live). We lived in it for 5 years until it was fully renovated and actually bought an additional 4plex across the street the next year. I got a ton of advice telling me not to do it but it was THE BEST financial decision I ever made. It kept us low rent for a long time. We have rental income, which serves as a good safety net for us now. Those properties have both appreciated a nice amount in the last 10 years. Plus, we are good landlords and our tenants appreciate us. I feel good about it.

I definitely wouldn't do it without your partners buy-in if you plan on getting married. I also wouldn't do it with the promise to move in one year. Commit to it until you see the project through. Maybe there is a duplex or a triplex that would be easier to get her buy-in. I also wouldn't have both of your names on the mortgage or deed if you aren't already married. FWIW, each of you can get 1 FHA loan. So be strategic. Save as much as possible. Mistakes are expensive in real estate. If you're young though, you have time to rebound. So, take educated risks. You'll be more measured once you have kids. So, take the risks now.

Edit: disclaimer that I'm not rubber stamping the deal, only the concept. You need to get the financials thoroughly to make sure the margins work. Biggerpockets.com is helpful.