When my dad was in his 20s, he would build a duplex each winter.
I grew up living in half of one.
I think you've got a great idea.
If you put enough down, then the rent from the other side will pay for the mortgage. Once that's done, you've got an income stream for the rest of your life.
The most important thing is to get good renters (not just now, but always, don't be a slum lord). Make them give you references. Don't rent to anyone that doesnt' have good prior rental references. "But I'm just starting out and have never rented anywhere" Tough tits, go rent somewhere else for a year and call me back. No you don't take Section 8 but you will take cash. Ask on the application if they have a vaccum cleaner, how else are you gonna keep my apartment clean? Write in the lease NO PARTIES and no parking on the damn grass. Safer to rent to married folks. Give a discount on your rent if a cop or hwy patrol or someone wants to live there, not much chance they will tear it up.
And when someone calls up and asks "will you work with me on the _____" tell them to pound sand. You need them to pay a full month's rent, and a deposit equal to that right from the get-go. If they are on good behaivor and don't trash the place, and give you a months notice before they move out, then they get thier deposit back.
If you're buying the place it might come with tenants and you can ask the previous owner if they are good or not.