@Hayden Hirzel I have been looking into doing something similar here in Southwest Florida. I currently do not own any property so this would be my first investment so it is a bit different than your situation. However, from what I have gathered you would still need a 3.5% down payment if you're able to use FHA. From people I have spoken to you can use FHA more than once but there has to be a valid reason such as outgrowing your first home, etc. Being as though you have turned your first home into an investment I do not see how you would be able to qualify for an FHA on a second home particularly a multi-family complex. Here is an excerpt from Riverbank Finance:
"In general, a borrower may have only one FHA mortgage loan at one time. If at some point they want to obtain another FHA loan then the first one needs to be paid off before applying for another one. However, there are exceptions to that rule according to The Department of Housing and Urban Development (HUD). They will allow a borrower to have two FHA loans but only under certain circumstances such as a bigger family size or because of job relocation.
Although the general rule only allows a borrower to have one FHA loan at a time, HUD also allows borrowers to have multiple government insured mortgages under the right circumstances, depending on their individual situations and what has changed since the close of their first FHA loan."
You can use the rent from your primary home and the rent from current renters of the MF you intend to buy as income when applying for a loan whether it be FHA or Conventional if you need help with your income and expense ratios. As I mentioned I haven't purchased my first property yet but I have been doing a lot of research so I hope I could help. If I am wrong or there are other strategies please share with me so I can learn as well! All the best!