You have room to add more than 225 more computers and it'll still be fine as a class C. No reason to subnet.
However....I'd recommend making a VLAN for your wireless "public" guests, so they can't cause problems with the main business network. A simple managed switch that can do port based VLANs would be able to do this. Or, depending on your access point...some of them support a feature which can VLAN each wireless client.
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