WRT speed and possible RAID:
Our current server is about 5 years old, running SUSE Linux. It has a 100Mbps network card and that has proven fast enough for our use. If we built a new machine now it would have a 1G network interface which might or might not help us. It doesn't make sense for us to have a fast hard drive array if we are limited by the network interface.
We are rethinking our entire setup right now. Our supplier dignosed our Linux hard drive as failing so now we are trying to retrieve whatever data from it that we can. We have a backup that is 1 day old so we are trying to recover what files might have been modified in the 1 day since. We have another drive installed in the server and ready to go, so when we are finished with the first drive then we will swap cables and hopefully be back up and running.
WRT Win7 vs. Linux:
Our ideas behind running a server through Windows is that any computer with Windows can become a server. If our server fails we can take the hard drive out or just take our last backup, restore to another Windows computer and be back up and running. As of now we have been out of commision for almost 2 full work days. We have 4 salaried employees that we are having to pay with a lot of wasted time over these 2 days. With Windows based machines we could have been back up and running yesterday morning.
WRT backups:
We can't get a Linux machine with its data drives in a RAID configuration, so we're thinking about having several levels of backup on our Windows workstations. Currently we have some USB external drives that we backup to and rotate outside of our office. We've had discussions about whether our backups should be complete mirrors or just incremental backups. With an incremental backup the backup continues to grow, because if someone renames a file or folder then the next time the backup is run it copies the newly names file or folder into the backup beside the ones with the old names. OTOH if we run a pure mirror and someone accidentally deletes a file from the server then the backup deletes the file from the backup. Actually we are now thinking about running both types of backup into separate hard drives, with the incremental backup only used in case someone deletes a file and doesn't realize it until days later.
WRT IT:
I am pretty much IT for our company. I build computers, troubleshoot things, etc. I have a lot of experience with Unix but I have tried really hard to stay away from Linux. So I know how to run Unix commands on Linux and it seems to understand most of them, but dealing with user accounts and such through SAMBA is something I don't have experience with.