Hi there,
Ok,
In your case you could for example use a network of:
192.168.0.0 255.255.254.0 (addresses from 192.168.0.0(network addess) to 192.168.1.255(broadcast address). As long as you use NAT it doesn't matter that these addresses are not all private ones. (You could also use the private class B net, but theres no specific reason for that in my opinion.
In a switched network there exist Layer 2 broadcasts. An example is an ARP request. This ARP request will be sent to each user on that special net. These Layer 2 broadcasts can decrease the available bandwidth on you net. That is one reason, why usually big networks will be divided into subnets after they reach some number of clients(this is only one reason, not the reason). I do not know rule for that, but someone told me that it will make sense to divide a network at about a number of 500 clients. If you will realize a loss of performance this might be one reason you should look at...