I use a Speedtouch 536 which is very similar to the one you are looking at. It will connect to Tiscali with the usual set up of username and so on.
Yes ethernet is generally quicker than USB but you may not notice the difference in any significant practical way.
The importance of a more up to date modem router is that not all older ones can benefit from the up to 8 meg. I cannot comment on whether your current one does or not. If you are going tp network then consider a wireless one which still can go hardwired or if you want hardwiring consider one with 2+ ethernet.