You don't need redirects unless you're changing domain names. Just keep the identical files on the old server for a few days, and change the dns info. Visitors will be directed to server 1 or 2 until the domain fully propogates, which can be a matter of minutes, or possibly a few days.
Most websites operate on shared ip addresses. I don't think anybody needs a dedicated ip unless you have a private SSL Cert or require anonymous
ftp. If you're really worried about it than choose a host that has a firm no-spam policy.
U.S. or U.K? - You'll have some latency crossing the Ocean, but not a big deal. Obviously, if the majority of your traffic is from the UK - than host in the UK.
as always, just my two cents.