1. Voltage is what determines the speed, so it will be just a bit slower, but since Lipos could deliver a lot of current (C rate) you will get better acceleration. (22.2V is nominal; the pack would stay at 24V or so for a while)
2. Yes you need to buy a LIPO charger; I have an RC charger/balancer IMAX8 that is working fine. You don`t need a BMS, but you will need a CA, or Watts up, or some stuff to monitor the pack voltage, you must never go under 3V.
Lipos are great, very small for the power you get!
There is a very useful treat to read about lipos in the forum, give it a try, it is very important to know how to handle them if not it could be dangerous: http://endless-sphere.com/forums/viewtopic.php?f=14&t=9170