Quote from @Nathan Esquenazi:
Should I worry about finding a property first and then finding a loan? Or loan first then property?
What is information I should know or be aware of when the time for purchase comes, or during the purchase phase?
Super solid advice above. To answer your specific questions. You need to get preapproved first. Note, there is a difference in prequalified and preapproved. You'd hate to spend time working through this, find a home run deal, then find out you don't qualify for the purchase. A preapproval will let you know exactly how much you qualify for and a good investor friendly lender will know how much of the rent from a multifamily they can count towards your income.
You want to partner with an investor friendly agent who can guide you here 🙋♂️. There are a ton of moving parts in a purchase transaction. BP has some good guides on the basics of the process but you'll want someone local who knows the areas and neighborhoods that will make a good rental property, after all this is an investment. Once you've identified a property and gotten an accepted offer you will want to do an inspection. Expect this to cost some money upfront, and it won't be cheap for a multifamily. $700+ for a duplex, possibly a couple thousand for a quad. There are also some add on reports you'll need to get from your home inspector to (hopefully) save some money on your insurance. Happy to connect if you have any more specific questions.