|Here are some hints though google is your friend.|
VoIP needs to be wired not wireless. You need the specs of this "app"
Wireless isn't as fast as wired nor as secure. Might want to get the security requirements for the project.
VPN appliance should have a client you can load on the mobil computers. We additionally have users, once authenicated to the vpn appliance, authenicate to the domain via a TS/RDP server.
Questions to consider:
how is the network going to be used?
will guests/contractors need network access?
required bandwidth for both incoming and outgoing internet access?