You definitely want to get pre-approved. If you have a property in mind, even better. Seeing the closing statement was eye-opening for me. If you're trying to use the BP calculators to analyze a deal, I found they are not accurate for closing costs as each state deals with taxes at closing differently.
Financing. Proof of Funds.
Once you know exactly what you have to play with, what down payment and reserves you have, then we can start searching for opportunities you can actually write offers on and most importantly close on.
If you plan on purchasing commercial 5+units and then it comes down to the income of the properties and how much money you have to put down. For residential (2-4 units) and if it is a flip type deal you want to work with someone who can fund smoothly with little delays. More often than not, a 2-4 unit flip type deal will find it hard to get financing depending on its condition and you will most likely get offered out by other investors putting in all cash.
Plenty to think about.