The proposed solution will not increase bandwidth support future growth or increase response time. Installing CAT 5 UTP cable and using network cards that supports speeds up to 100Mbps will not increase bandwidth within this network.
To increase server response time i guess id have to say create a server farm Rather then using one Server. Not to sure about this one.
Installing a switch rather then a hub would decrease the amount of collisions within a network and increase response time. Also installing routers within the network and creating subnetworks will decrease the amount of broadcast going across the network also increasing response time. Also with the router you can segregate unused address space for future use. And Be sure these routers and switches support 100mbps or higher to achieve your goal of increasing bandwidth.