Hey @Gabriel Spaulding, welcome to the BP Community!
Oh man, I don't even know where to start! haha
Really, you just need to educate yourself a bit more, my friend. We're here if you have specific questions or still don't understand how something works after looking into it yourself. However, your last questions tell me that you haven't even read a book on investing or property management. Start with Brandon Turner's "Book on Rental Property Investing". He also has one on "Managing Rental Properties." Also, listen to the first dozen or so BP Podcasts (I think there is even a beginner-focused separate podcast now too).
Even if we simply gave you all the answers now, you would not be ready and you would likely forget them by the time you were.
You have some very cool ideas but first you need to get the basics down. Slow down and build that foundation. This is not a race and it's certainly not a quick way to make money. Follow the same process we all did starting out and be patient but persistent. Honestly, if you're passionate about real estate, the learning part should be really fun for you and there are plenty of resources out there to help you with this.
To answer a few of your more specific questions. No, you cannot buy MHP with an FHA loan. You also likely can't build some tiny homes on your SFH zoned land unless the municipality allows it. Create an LLC after you buy. I do not have the answer to your very general question regarding whether to buy a triplex, quad or MHP. Remember, the more info you can provide us in a concise form, the more likely someone might have an answer that helps. Specific, to the point questions get answer more frequently than general, drawn out questions. Help us help you!
And please, feel free to reach out to me anytime if you have other questions or just want to chat!