Building a small network in Apple environment?
There are several ways to accomplish this. Let's list your requirements:


Multiple Macs.
Shared files between them.
Wired network.
Backups either online or local.
Remote access to files.


While OS X Server is certainly useful here (especially if you wanted a VPN), it isn't necessary. Assuming all of your PCs are on the network, I would set up a NAS (network attached storage device) and locate my files there. Many NAS also have the ability to share files out remotely. 

Alternatively, you could load Dropbox, Box.net, or some similar service on each device, and share specific folders to each user account. This would allow you to more easily integrate devices external to your network into your file sharing system. Each such service offers varying tiers of free space, and you pay as you add onto them. An added bonus would be the ability to roll back file changes, or recover deletions (at least DropBox has this feature.)

As with any setup, your mileage will vary.