Hi Adelaide! My wife and I live and invest in SW Michigan so we are across the state from you. We have a few single family rentals and we closed on an 8-unit apartment building about 6 months ago. I completely agree with Amir that anything 5 units and above moves you from residential to commercial and has a lot of differences. Here are a few thoughts:
1. I highly recommend the Bigger Pockets Multifamily bootcamp. I just completed the winter session but they are doing another one that starts in June. There were a lot of things that I learned that I wish I would've known before we did our first multifamily deal.
2. How you determine the value of the building is very different from residential real estate which uses comparable sales. You need to know the net operating income (NOI) and divide that by the cap rate. Because of that, it is critical to get accurate financial statements from the seller. You also have to make sure the NOI covers your mortgage payments by a set amount that the bank determines (e.g. NOI is at least 125% of mortgage which would be a DSCR of 1.25)
3. Lending is through a commercial lender. This is a lot more relationship based so it is good to start reaching out to commercial lenders before you have a deal. We found a great deal and almost lost it because we struggled to lock down a commercial lender in time. Small local banks and credit unions are commonly used for commercial lending.
4. Due diligence is a lot more intensive and consists of a document review period, an environmental study, etc.
There are many more differences, but this should get you started. I also recommend Brandon Turner and Brian Murray's 2 part book series "The Multifamily Millionaire" as this goes through a lot of that. Good luck and I hope it works out for you! Multifamily is a great way to scale more quickly and efficiently and despite our learning curve and many mistakes, our first multifamily property has still been a huge success!