Boss wants me to build a new server

First question. Do you want to be on a network domain? I should hope not. If you use windows server (wich does not fit your needs) it must be a network domain also it's a 1000$ for the os and an aditional 100$ for each computer that simply connects to the server for basic file sharing. I don't think you need to run a true server OS for a simple filesharing and database. Unless that software requires you run windows server. (Most don't)

How many computers will be connecting to this server? Reason is if it's more than 10 you do need a server OS or linux. Standard windows has a 10 user limit for file sharing. (Must be pro editions not home)

ECC memory is best used for server that NEVER EVER get turned off. If you plan on shutting it down at night NON ECC is fine. If you don't need large storage volume then SSD. Otherwise A raid array for Traditional HDD. SCSI is overkill for a file server and I don't belive has many advatages over SATA

Here my suggestions for a true server.

Tyan brand M/B
Xenon is a good choice. Probably the 5550 Fi i rember right
WD RE4 hardrives. In a raid 5. Using At least 4 drives.
Raid 5 gives performace incress over 1 drive and it is fully reduntant to the point that one drive will fail and the computer will still continue to run without that drive.

If it's a very small capacity file server than 2 SSD in raid 0 or 3 in raid 5

ECC memory only if it never gets turned off at night and has a heavy load on it all day. Otherwise standard is fine. NOTE: ECC is also called RDIIM

Onboard video or if not built in than a any cheap video card work such as an nvidia 8400

Powersupply. Pick the most reliable one you can find. And possible one that you have spares for in shop. If it goes out theres no powering the system till the part arrives leaving your buissness SOL for a few days. Also there are DUAL reduntant power supplys for custom servers.

Put this thing on a huge Battery backup. Somthing like 1000 watts. The last thing you want is the server to go down in the middle of database operations and currupting the whole database.

While designing this keep this in mind. If any one part breaks how much down time will it have? Can the company afford a week without the server while a new PSU/MB/HDD is shiped from newegg? Many companines used standard workstation parts for interchageability or they stick with dell servers becuse of the NEXT DAY service. Trust me it really is next day service too. Consider buying a refurbished server from dell outlet.com They are way way cheaper than new and still have a full 1 year warrenty wich you can upgrad to 3.

Just keep in mind what kind of position would you be putting your buissness in if this server broke.