1. Turn off Network Manager, setup ifcfg-eth0 and ifcfg-eth1 directly
2. Turn on net.ipv4.ip_forward, blah blah blah
3. Setup iptables This website can help you. No need to use openvswitch but use bridge is good enough. For your case you do not need to use bridge actually.
Note: Better to skip those GUI and configure them via console directly.