My suggestion would be to talk to the different agencies (if there's more than one) and decide which one you want to use. Once you make that decision, they'll tell you everything you need for your home study. I would actually wait on physicals if I were you; I only say that because for ours, we had to take the agency's form with us for our physicals to have the doctor fill it out.
Our home study cost $1300 and took a few months, but a good part of that is just waiting for various things to happen, it's not as bad as it sounds. I asked our adoption counselor ahead of time if she wanted us to have a room ready, explaining that we never got it ready because we were going through infertility and it was too painful to look at an empty room. She said, "heavens no!" They just wanted to make sure the room was there and that our home was a decent, safe place for a kid to grow up. Don't drive yourself nuts cleaning, just make sure things are tidy and neat. (We DID drive ourselves nuts cleaning, and even though she was at our house for about three hours, most of that was watching some adoption DVDs and discussing them. The actual home tour was five minutes or less.)
Remember that laws are different for each state, so you may need to provide more than others have, or less. Your agency can help with all of that. So far, even though we just had a BM back out on us, the experience as a whole has been wonderful and I look forward to the next match. I wish you luck on your journey! It's quite a ride!