Wot else do I need to buy with Windows Server 2003 apart from CALs?

Im getting a file/application server with Windows 2003 server on it for a small business office (less than 30 PCs+devices). Im also getting 30 CALs and the total runs to almost $3k.

Is there any other MANDATORY software or license i might need. (Im only using this machine to share files and construction software, no hosting or anything...and im on a secured network with a firewall)

Unless you're running terminal services, make sure you're getting Small Business Server 2003 Standard; not 2003 Standard Server. (For a relative novice, the wizards are easier than manual creation of your domain). You also get Exchange, Remote Web Workplace and Sharepoint built in. (Even though you think you won't use them now, they're a huge added value, and you can light up these services later if you wish. Without Small Business Server, you'll have to pay out the nose to upgrade to these services.
The software comes with 5 CAL's built in, so you'll only need 25 more.
Other than that, nothing more is "required". (Though antivirus/antispyware would be a good idea).

You need the CALs, that's it. It would be cheaper (when you factor in everything your getting, including MUCH easier to manage) if you get Small Business Server (SBS) 2003 instead of Windows Server 2003. SBS is intended for small businesses and includes Windows Server, Exchange Server, and R2 now includes WSUS as well.

SBS is good for businesses with up to 75 users - if you reach that point you would get the transition pack and upgrade to standard versions of Windows (the cost difference is minor; the transition pack is intended to cost about what it would have had you never bought sbs+transition pack and instead bought full, regular versions of Exchange and Windows.

SBS also uses Wizards to help you manage the server - it makes things MUCH easier for non-admins to administer.

What I consider required for any business server:
RAID for the hard drives. Understanding how to back up the system. sufficient RAM (2 GB for SBS and 30 users).

More reading:
http://www.lwcomputing.com/tips/static/s...
http://www.lwcomputing.com/tips/static/b...
http://www.lwcomputing.com/tips/static/d...
(understanding how DNS works in an Active Directory domain is vital to a properly working network).