1. "I'm new to vlans, but I'm thinking to set one up" - If this is a production environment and you're setting up a VLAN just for the heck of it then stop. Never do anything without having clearly defined needs and outcomes.
2. "I'm wondering if I can assign the vlan any network address I want" - Why would you want to do that? Wouldn't it make more sense to assign an ip address from the network range you're using internally? What would be the point of assigning it a random ip address?
3. "I'm wondering if I can set the vlan so these computers will get the network they're already looking for" - Why would you think these two things are related?
My suggestion to you is to go read up on VLAN's; what they are, how they're used, what layer of the OSI model they fit into, what purpose they serve, etc. If you're doing this as an educational activity then that's great but first get a foundational understanding of VLAN's before you go implementing them.