Long or short term?
Check in with an accountant if you have an ISA; the US may not recognise it and you'll have to pay tax on it. Honestly, depending on what you have (pension aside), it might be simpler selling everything when you move.
You have to file a tax return! Your company doesn't do it all for you.
I'm in Canada, but I have some knowledge of the US (I actually own a couple, soon to be one, rentals in TX).
There is
https://www.fatwallet.com/forums for a lot of good stuff.
If you have an Amex, do a Global Transfer. If you don't have an Amex and it'll be 6 months (I think) before you move, get an Amex.
Not sure, but Barclays exist in the US; you may be able to get some kind of jumpstart on credit there. Worth a try, if you have a Barclaycard. Oh, or HSBC - HSBC Premier is good for country hoppers.
Check IP Daley's thread on cell stuff for cheap phone plans. GSM phones will work on some networks (AT&T) but not others (TMobile), I believe. In certain areas, there IS no alternative internet provider. Often no different electricity/gas provider, either.
Remember to drive on the wrong side of the road :)