Getting comparables for mfh seems more difficult than sfh are they comparable to each other? Not necessarily comparable, I'd typically charge more for single family house versus an apartment unit because people will pay more to have a whole house to themselves.
What questions should I be asking the current landlord and/or real estate agent? Do you have an agent that can ask these questions for you and help you determine the questions to ask? I would ask them for the current rent rolls to ensure the tenants are paying on time monthly, as well as the leases to see when they are up and the terms.
Is it rude to offer below asking and then ask for seller finance? No, not rude. They can always counteroffer and the worst that can happen is for them to say no.
When running numbers should I be running each unit individually or the whole complex as 1? Whole complex
Am I going in to RE too fast by trying to buy a 4plex as my first deal and out of state? No it sounds like you're being thoughtful and not just jumping in head first! I think it's a great idea.