Citrix and terminal services

Hello all,

This is my first time deploying Citrix and TS. I am running a native Windows 2000 AD. All the remote users (10-15) that are going to access the server are W2K/XP clients.

1) Do I need to purchase TScals for Application Server Mode?
2) For security. Should I run the terminal server as a stand-alone server, a member server in the domain? or a different domain with trust-relationships between domains?
3) Can I use a Windows server 2003 TS in a Windows 2000 domain?
Lastly, any good articles or links to Citrix setup would be very helpful.
Thanks,