Be sure to let the limo company know immediately if you have special needs, so they can make the appropriate arrangements. This is especially important if you or one of your party is handicapped, or if a very young child will be sharing the limo.
If you prefer a newer limousine, ask the limo company the age of the vehicles in their fleet. If you don't, you may end up with something older than you're comfortable with. On the other hand, the company may well offer lower rates on its older limos.