Self hosting email on non-mission critical domain for learning purposes might be okay if your intention is to get into the industry. Self hosting email for others on more production like setting you’re going to find yourself in a world of pain.
All it takes is one missed email (be it not making into their intended recipient’s inbox, or them not receiving an important notice in their inbox) and you’re never going to hear the end of it.
You’d also be liable for content your users send out from your servers — and I don’t mean the spam type, though if you get your IP blacklisted, your provider may want to have a word with you.
I’d strongly advise against going down this path, but if you do, be sure to have ways to legally shield yourself from any sort of potential liabilities.