Setting up Samba is easy (if you throw an afternoon - well, less, probably - at it and read the docs carefull, that is). Correctly configuring ssh is much harder (with the protection stuff, that is), so learn Samba first.
More important, Smb is designed for what you want. Telnet/ssh isn't.
Anyway, if you do want to do ssh (NO telnet please, it's obsolete), make sure your firewall blocks any connection attemps to the server from outside your LAN (your firewall docs should tell how, this shouldn't pose a problem). This is a safeguard to make sure nothing gets through.
Also, your server should block any such attemps (redundancy is a good thing in security). This should also be in your docs, and differs per server (if yours can't do this, get another one).
Last, make sure every account has a decent password. If anything gets through to connect (ie by taking control of one of the clients, or another way of bypassing the firewall and server policies), it still can't do anything that way.
In short, read the docs. From front to back, preferrably. Building a server takes work, a misconfigured server is worse than no server at all.
Ssh makes you log in as a normal user, so there is no real way of locking you in a certain directory (AFAIK). You can, of course, restrict ssh logins to a single user, with limited access.
