@1: only the server port needs to be accessible, although some routers have problems forwarding back and forth UDP traffic; YMMV. Try tcp mode if you think there's a problem with your router
@2: you're asking for trouble if the LAN IP ranges on both client and server side are the same; I'd highly recommend to change either side. People have gotten it to work without changing the IP ranges but this is for networking experts only.
@3: I'd use a tool like 'nmap' , although a UDP port scan is not very trustworthy. If you've configured OpenVPN in 'tcp' mode then a
telnet <VPN-server-IP> 1194
should also report *something* other than 'connection refused'.