Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Configuring a DSL modem for usage is one of the most exacting and difficult configurations that could be aimed at, for sure.
As for having the Netopia 'pass the Internet thru its RJ45 ports', it doesn't quite work that way usually. The phone line provides internet service to the DSL modem, which then provides Internet access through its ports. The speed of those ports (RJ45-type Ethernet) then determines how fast the Internet access allowed is... but usually those Ethernet ports are inherently faster than the DSL service provided by the phone line, so that is not the limiting factor.
As for the DSL configuration, you need to have DSL service on your phone line from a DSL/ADSL service providing company, and the configuration of the Netopia modem will depend upon what the company providing DSL is.
You can disable wireless on the Netopia no doubt.
You could disable DHCP on it also no doubt.
But!: there is an appropriate set of settings to get a DSL modem to work with a DSL line. This set of settings is matched to the corporation that provides the DSL service. It must be set up to the letter, before the Netopia will work at all. If one of the settings you desire conflicts with that set up procedure in any detail, DSL service may not work.
On the other hand, if you simply wish to have the Linksys box be the WiFi router and the wired hub/router, that's easy enough. In fact you set up the Linksys box to serve that function, not the Netopia box.
And also hopefully, you can disable wireless on the Netopia box and still have DSL service, I feel confident.
I cannot give you the steps until I know the DSL provider on the DSL line. Without that information, the task is impossible.