going to be upgrading from a 55 to a 72 bow

[lms]

So I am looking to upgrade me 55 (no sump) do to the fact that my fish have grown out of my existing tank. I just picked up a 72 bow that is drilled in the middle of the back piece of glass.
1) I have never used a sump and was thinking about trying to make my own, and was not sure what size pump I should be running?
2) When I make the change can I use new sand with out upsetting the tank?

thanks,
Lis