With a 7:45am flight, DME will pick you up at 4:45, plus or minus 15 min. Remember, that will be the time DME leaves your resort, not when it gets there.
Since RAC doesn't open until 5am, you will not be able to use that service. You will have to take your bags on the bus with you and then check it in at MCO.
DME drops off on the same level as pick up, but more centrally located. It's not at the end like DME pick-up is. You will have to schlep your bags upstairs to your airline counter. There are luggage carts nearby that you can rent if you need one.
Steve