1) Are you asking how many contacts you can send one SMS message to? I believe it's 10. However, you could create a group within your address book and send the SMS to that group. I am not aware of a limit on that.
2) I don't believe there's a limit other than device memory. I've heard of people with 3,000 plus contacts on their device.
3) Check out BlackBerry FAQ - BlackBerryFAQ
, browse these forums, and check out Stinsonddog's tips : Stinsonddog's Blackberry Tips and Tricks ‚Äé(Blackberry Tips & Tricks from the Mods)‚Äé