It's absolutly normal:
- first, you shouldn't change the server-bridge.conf file manually (exept if you want to push additionnal routes, but I don't think you need to)
- second, you don't have to change the firewall configuration on the server, everything will be set correctly
- Third, the network behind the client is nated, so it's totally normal that the server cannot ping them. The server need to know the gateway for this network. So choose a fixed IP for your client, and add a local network (in the server-manager), setting the network ip and netmask, and the gateway will be the IP you've choosed for your client.