Hi, I may be able to help with one of your questions.
Internet dilemna - I have an adsl connection which currently I connect to through a usb modem. The difficulty I am having is that this modem is not easy to get working under linux (speedtouch 330). I have managed to get it working under ubuntu desktop but not server. I would much rather use an ethernet modem due to the ease of setup aspect, but the problems with that are the mini-itx board I am looking at has 1 ethernet port (internal), and 2 pci slots - both of which I intend to use for other purposes, and also it drains a little more power and takes up another power socket. How this relates to linuxmce - if i managed to get the usb modem working, would it be easy to configure the firewall etc to use a ppp connection as external instead of an ethernet connection?
Your layout should look like this.
Cable/DSL Modem -> Wired Router -> 4/24 Port Switch -> All things in your house go to your switch. Although I have almost no experience with DSL but from my understanding it should layout the same. If not I am sorry I was not able to help.