I change Disney resorts all the time and have done so for years, so I will try to be of some help.
You do not leave your bags in the room if you are transferring luggage, you call luggage services and very quickly a CM will be up to take away and tag your luggage. Your luggage will be transferred to the new resort by the latest 2-3 PM. It is customary to tip the bellman for this service $1-2 per bag.
When you get to your new resort and in your room, your bags will not be automatically in your room (except at the value resorts) at all other Disney resorts you must call luggage services and your bags will be brought up to you. Tipping the bellman the same amount is customary.
I have found it is best to check into the new resort first thing in the AM, you will have a much better chance of getting any room requests. I know many others think this does not matter but I have had too much success, too many times with checking into the new resort first thing in the AM, to believe the rooms are firmly pre assigned.
I would recommend moving your own luggage since you will have a car. Many times when we arrive at the new resorts a room will be ready and it is nice to have your luggage right there to unpack vs waiting until 2-3 PM for it to arrive from the first resort. Don't get me wrong, Disney makes luggage transfer very easy but when I have a car I always take my own luggage. It is no harder to call bell services to load your luggage into your car than it is to call bell services to transfer your luggage.
Have a great trip!