Most of those questions can't be answered by us. Why not ring the sales people and ask them?
The reason they are no doubt asking for a name and address is so that the call can be logged in whatever system they use.
You do not have to use Virgin.net as your ISP there is nothing to stop you using Freeserve. When I bought my Mesh PC the Virgin stuff was just an exe on the desktop you could run. Needless to say I didn't.
There will no doubt be machines sold in the future that have the higher speed processors. But that will always be the case so I can't see why impact it will have on you.
Can't see any reason why the Keyboard and Mouse you have would not work on the system - but I also doubt Mesh would give an answer on that one.
As for point 8 very few PC's come with free software you actually need. Not something you should but at the top of the shopping list.