1 Terminal Server can easily handle 6 concurent users w/o a problem so it wouldn't need to be run on a seperate server unless you're trying to run Exchange or a big SQL database on it--then I'd say pick another server.
The diff btw Remote Admin and Application Server is primarily licensing, with a few tweaks. Remote Admin only allows 1 Administrator (i.e. in Admin group) to access the server remotely at a time but requires no licening. Application server allows as many people to connect as have Client Licenses. Since all your machines are 2000, you won't have any problems since 2000 includes a CAL for Terminal Services.
Once you install terminal services, it is important that you use the Add/Remove programs from the control panel when adding new software. Doing this procedure puts the terminal server in a special installation mode so it's available to all users. 90% of the software loads fine w/o any tweaks. The other 10%, including MS Office, sometimes requires you to download a new library or two to run in a Terminal Services environment.
Last time, Download the latest Terminal Service from Microsoft, rather than using the 'create disks' option. The latest TS Client is the one they include with XP (although works under 2k) and is far superior than the previous client, imho.
Iota