Thanks for your suggestions. I do have a ASUS router with openvpn server. It does provide some settings which make it very complicated to use.

2, 3, 5 will be added.
4 should already be done, I think.
6 Tun and Tap will be investigated. I think this will be different scenarios.
7 should be done in client side, not server side.
8 We did you upnp to open ports but seems this is never reliable. Less than 30% can be successful. Most routers will have upnp disabled.
9. 10. 11 Yes.
12 I am not sure if this should be enabled. My ASUS router surely have this. This changes the application scenario. I’d rather to add if vpn should be able to access the local network. By default, it only can access Internet.
13 Good suggestion.