1. Pretty much. Open a ticket to billing and they will inform you of the process.
2. I would go the resellers route. It just makes it easier to manage that many accounts. It allows you to alloacte based on the needs of the individual account. I have one and dont resell anything.
It really is tough to say. Often it is no noticable down time at all. Each case is diferent and I have seen mixups where the site was down for 2 days. Nine out of ten people will not see anything at all.
Please allow about 7 to 10 days total for the transfer to take place. During that time there should be minimal downtime. Upload your site here and it will minimize that time down.
The post below has some good tips.
Alan,
Changing name servers is not the same as changing registrars. I see you changed name servers
That part is taken care of, you cannot change registrars to have us as the registrar as we do not have the capacity to control .co.uk domains yet.