Hi Bernd,
1 Since DHCP service is running on the 1st router, the Linksys router’s WAN interface should be set to automatic.
2 The router lan ip address (under setup/basic setup) refers to the router’s LAN ports. This can be set to anything you want the LAN network to be, it is usually set to 192.168.20.1. When you run the command it will set the ip address to the value as indicated in the command box.
3 You should use your ISP’s DNS servers or Google’s servers of 8.8.8.8. Gateway refers to the gateway of the LAN port, which in this case can be left blank.
4 The router’s ip address maybe changed if you use the command based setup, but if you used the built in setup method then the ip address will not change.
After a user connects to the router, he should receive an ip address on the 192.168.182.0 network (by default).