I'm not sure what your local options might look like with a small community bank or a credit union. Depending on your tax returns, that might be an option. Pros- the loan costs for this will be less, depending on their underwriting approach (creativity and aggressiveness) then they might do the first-year interest-only allowing you to rehab and put in long term financing without having to refinance. Cons- depending on your personal financials, qualifying might be more challenging and the loan might not amortize over 30-years.
Another alternative would be a business-purpose rehab loan (fix and flip/fix to rent). Even though it is a 4-plex, it still falls in the same bucket with similar loan structures as if you bought a single-family rental. Depending on the rehab budget, you would be looking at up to 90% of the purchase price, 100% of the rehab, capped at 75% ARV. Pros- flexible underwriting criteria that will only look at the transaction and less at your personal financials. Cons- the loan costs will be higher, the loan will have a max one year term, and you will have to refinance.
The flip side of having to refinance is that you will be able to use the equity that you build in the property through the renovation to pay for the loan costs and possibly pull some cash out.