19 year old house hacking

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Im 18 turning 19 in 2 months and I really want to get into real estate investing as soon as possible. I am freshman in college and will graduate debt free. I also have been building my credit since I turned 18 and it's at 705 right now. I've read plenty of books, listened to tons of podcasts, watched tons of youtube videos, and practiced running numbers and finding good deals to the point where I understand most things and I feel pretty confident in being a landlord and start house hacking. I feel as if I learned enough to start and I will learn the absolute most by getting my foot in the game which is why I want to start now. 

Here is my plan. I plan on using a fha or fha203k loan depending on the property i'm buying, to buy a multifamily within the next year and rent out the other unit(s) to cover most or all of the monthly payments. I work a part time job bringing in around $1,500 a month after tax that I am saving for vacanies and repairs, etc. My girlfriend will move in with me and will also save up for vacanies, etc. I got kind of creative and convinced my girlfriends dad to say yes to cosign the fha loan and give me the money for a downpayment and closing costs (if needed) as well. So i feel like I will be able to qualify for the loan when I need to get one. I plan to refinance the loan when I graduate and get a stable job so I can get my girlfriends dad off. My question is do you have any advice for a young first time home buyer? Do you think this is a good plan? Am I missing anything? Anything will help! Thank you.