Preferably two separate boxes for the servers. But it is possible to have it on one, but security issue abound especially with domain controllers.
On the positive side, like I said, the TS need not be a super server. A 2.8 Ghz
single process, 2G ram, with 2 72 gig drives mirrored, preferably scsi, preferable dual power supplies will suffice; a cheap monitor or a shared monitor via a KMV device will do, as no one will be using the TS server console execept for setup and maintenance. A deluxe TS server would have a raid 5 array on a hardware raid adapter, with a min of (3) 36 Gig disks.
One VPN enable firewall is all that is needed at the office, along with VPN software on the remote side or cheap VPN gateway routers. Personally I would not run OS based VPN except for a large office, VPN equipped gateway router are fairly cheap, require little maintenance, basically nothing to go wrong. Netgear has VPN models, Sonicwall is another, I have primarily used Sonicwall units for the office side; your netgear my be usable if it has VPN capabilities. If you have not setup a VPN system before I would recommend you get a consultant to do the initial setup, getting the system going can be extremely aggravating for a novice, (been there/done that 6 years ago). VPN initially is like learning a foreign language, difficult at first, easier as time goes on.
I use Linksys BEFsx41 or Befvpn41 for remotes if the remotes are stationary machines, Software VPNs clients for mobile laptops, though they have small USN VPN routers for laptops (linksys). One static for the office would be needed, the remote with work with either static or dynamic broadband addresses, on cable or DSL. The line speed need not be super fast, as key strokes and video updates are the main traffic( 768k down and around 278 up is sufficant).
With 5 users, I would have DHCP setup, with static addresses reserved for the five users and the TS and regular server, and the office router; a few static address are very easy to manage, the DHCP server could dole out dynamic address to a user from outside the office, who brings a laptop in.