Wired and Wireless Network setup

Right now at work we have a wireless network set up for internet access and file sharing amongst the computers. We have 10 computers now and will probably be adding a few more in the next year. We are going to set up a gigabit Ethernet network to help speed up the access and transfer of network files. Is there a way to set this up so file sharing only happens across the gigabit network and internet access only runs on the wireless? I really don't want the internet use eating up bandwidth on the gigabit. We have some important software that has a central database that needs to be accessed by all the computers and I would like to reserve the gigabit for that. I am assuming I don't have to hook up the gigabit router to the internet connection. So that will keep internet traffic off of it. But what is to stop the file transfers from going over the wireless instead of the wired? Is it set up to automatically take the path of least resistance/highest bandwidth?

And as a side note, what are some good brands to look at for gigabit routers? Do I need a router or can I just get a hub?

Thanks in advance, I know I always get good answers from the people here.