I want to use the Community edition of OpenVPN to create a server for unlimited users.
[*]Can I do that using the Community version?
yes
[*]How many users the Community version supports?
in theory unlimited, but it depends a lot on the hardware; a single openvpn *process* can handle 100+ clients (depending on client network usage); you can run multiple openvpn processes on a single box but you'll end up using different protocols (udp/tcp) and ports
[*]Can I use the OpenVPN client on Cellular Modem/Routers?
some routers and switches have support for OpenVPN, esp the ones that run openwrt or dd-wrt; what kind of cellular modems are you thinking of?
[*]Specipic Routers should be chosen in order to have the OpenVPN client connect or is it generic that supports all clients?
some cheapo switches/routers don't correctly forward UDP traffic so that can hinder OpenVPN but in general any generic switch should support openvpn. If they don't it's the switch that's broken, not OpenVPN.
