Simple data sharing server

Sorry for the clearly noob question. I’ve read through other recent threads on Lion server and the xserve etc., and I’m not really sure that I know much more than I started.

I have been managing a very simple OSX Server in a research lab, and I’m looking to set up a new one in the near future. The current setup is a mac pro running OSX Server, with several rack-mounted large RAID drives (both eSATA and FW800) and a backup-UPS battery powersource. The primary function is to have a central storage space for large amounts of imaging and other data available to multiple machines both locally and off-site. Perhaps it’s working as our own mini cloud for 20 or so users. We also manage a common iCal and Address Book on the server, but its primary function is data storage and network sharing of the data.

As I’m in a position to start over again to put together a new system, I’ve been looking at options. xServe is gone, and from reading the thread on the Active SAN metadata controller I don’t think that it is what I’m looking for (right?). If I understand correctly, Lion will have some relatively simple server features (likely) built in.

These are my questions:
1) Since data sharing it the primary function, is a server really what I want? I know I could do something with a simpler networked storage device, but it seems to me that a server does a better job of controlling access and managing multiple RAID drives.
2) I have some experience with OSX Server, but no experience with any other sort. Should I be looking outside the Mac-verse for a simple data-sharing server that will work for both Macs and PCs.
3) Is a Mac Mini running server a viable option? One advantage is that I could mount this to a rack. Still have to find some sort of power backup solution. My main concern is the speed by which the data can be shared over the network with other machines. I suspect that the real bottleneck is the network connection, not the mini, but I’m a noob and guessing here. It seems to me that the method used to connect a mini to the RAID drives would also impact this seriously. I don’t see any eSATA ports on the mini, and that should be the fastest, right?

I know that there are a lot of serious server administrators here, and these sorts of noob questions are likely very naïve. I appreciate any advice.

Thanks