Here are a few things I wish I had known before going to TDR. Hopefully these may help others, especially if arriving after the Welcome Center has closed (as we did):
Shuttle bus for official partner hotels:
When you exit the JR Maihama station, the bus stops in front of the station (for numbered buses) are for city buses - NOT hotel shuttle buses. You will need to follow the curb around to the right, and just past the taxis you will see the hotel shuttle bus stop (overhead sign in English and Japanese). The buses (silver with Mickey-shaped windows) have signs on the side identifying to which hotel they go. Each hotel has its own bus.
Hotel Shuttle bus to monorail station:
My experience was that the buses leave the hotel pretty frequently. About half the time the bus was waiting when we got outside, and then left a few min. later. The other half of the time, the bus arrived a few min. after we had, and then left a few min. later. So don't worry, it's not like if you miss one you'd have to wait 30 min. for the next one.
Buying monorail tickets:
Monorail tickets can be purchased from vending machines in the monorail stations as you enter. If you want to buy a multi-day ticket, do NOT buy it ahead of time from the station machines. Buy it on the day you will first use it. Its usage period will be dated from the day of purchase, not the day of first use. Learned the hard way, trust me (although station staff did exchange it when they realized what had happened).
Although you can use other cards such as Suica, I believe the monorail multi-day ticket is the best deal if you will be there for several days.
If your first day will be spent at Tokyo Disneyland, and you won't be leaving the park and returning, consider using your hotel's free shuttle bus to the JR Maihama station. From there it's just a short walk to the park gates, and you can use the shuttle bus back again. Or, just get on the monorail and enjoy the ride.
Again, I hope this helps somebody, and if anyone has any other tips or corrections please add on.