Keep the mask natural class C to give yourself room to grow in each of the locations and route traffic between the sites.
I agree with mister bees that a flat network of 400 PC's is not a good idea in today's networks.
Not knowing how your fiber will be strung together, its difficult to arrange a proper topology, however, if its arranged in a manner to have at least one redundant path, or multiples in a mesh, that's the best scenario.
The mesh would ideally look like this:
192.168.1.x=========192.168.25.x
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| \ / |
| / |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
192.168.30.X 192.168.38.x
You can use weighted static routes for something this small, or you can use RIPv2 or a tiny area of OSPF if you think RIP is a dirty word.

Many layer3 switches can run dynamic routing protocols if you can do it, so I do agree with mister palmer on the idea of purchasing a Layer 3 switch for each site..be careful as some may require a higher end license cost/switch.
Each switch would ideally have at least 1 gig, or a gig Etherchannel/multilink bundle to each location..check your distances and fiber types to determine which Gig optics to obtain (LX, SX, Zx, etc).
I hope this helps.
-HH
Real trouble call:
Customer: "I have a huge problem. A friend has put a screensaver on my computer, but every time I move the mouse, it disappears!"