I have a fonero unit that on which I have booted OpenWRT and used successfully as gateway router.

I want to now use it as a gateway off  a local WiFi service. The downstream side is then connected to a conventional 100bT WAN router with downsteram side hub and WiFi AP (eg a cheapo Belkin unit).

So I need to do this:

WAN-side: port ath0 (WiFi, operating as client, auto-channel sensing but connecting to specific SSID; DHCP client when up to get IP address etc)
(got a nice antenna for this side - I think that it gives 21dBi...)

LAN-side: port eth0 (100bT, operating as gateway on address 192.168.0.1/24, DHCP server starting at 192.168.0.10)

Routing: whatever, per usual ISP access gateway router (RIP or whatever) - but without static routes because of the DHCP on the WAN side (router addressed through 192.168.0.1)

No bridging, firewall or filtering necessary. The firewall is in the downstream access router.

I'm proposing to use this 2-hop approach because I cant have the downstream access router doing upstream DHCP - becuase then I cant get into the fonero as the address is always changing...

My questions
1. How do I designate ath0 as the WAN port?
2. How do I get (a) ath0 to DHCP AND be a client AND (b) get eth0 to DHCP AND be a server.

Any help greatly appreciated.
Thanks
Nick

Firewall: