Hi Melanie,
Well, that really is a loaded question as it all depends on how much money you want to spend, what kind of OS you want, are you Microsoft, Linus, Mac, etc. It does sound as if you have experience with Mac, but it is not user friendly with AC, although you can do it.
If you are starting from scratch, then you may as well do client/server. Everyone on here knows I prefer that route, but it is really no different than P2P except that everything is on the server. In P2P, you can have everything on the "main computer" as you have to designate one computer as the "server" with AC in order to run it correctly or at all.
Again, even if you purchase a fancy server and a server OS, doesn't really change anything other than your AC is running on better hardware. Server hardware is just better in almost every aspect of a computer as far as speed, reliability, etc. The OS, though, is really not that useful unless you allow it to be a domain controller or run the network depending.
There really is no other good option than to have your server onsite. I suppose you could have someone host it, and if they are very good and inexpensive, that has its advantages. But, I would think most people keep it in house.
If I were setting your system up, I would go with the Dell Optiplexes (which are fine) and set up a low to mid end Dell Server with a RAID. I would then use SBS 2008 as would give you all sorts of business advantages: Exchange Server, Sharepoint, SQL Server 2005 all included which would cost much more if you added them to, say, Windows Server 2003 or 2008. It sounds as if you would at least have to have someone come in and set up your network if you aren't comfortable doing that. But, the Small Business Servers are loaded with wizards that make setup rather easy. Installing SBS would be simple. Configuring it would be a little harder. It is relatively easy to attach each client PC to the domain as the wizard for that is foolproof.
Wired vs Wireless: I am simply a wired person. It's faster, and you never lose your connection. It's also more secure, although that isn't much of an issue anymore. You can easily do both. You can set up a wired network and then have a wireless access point if your doctors were using notebooks.
Backup up online vs no has really nothing to do with your type of network. It is imperative to have some type of off site backup. You can really do both. If you have a server, it is good to back it up nightly. You can always do AC backups on top of that.
It's certainly cheaper to go with P2P. If you had 8 Dell client computers, that is less money than 8 plus a $3,000 server and around $1,000 for the OS and CALs. But, the Foundation setup above would make it affordable.
Let me know if I can be of anymore help.
