I understand your feelings about using to a windows machine - I have always done my best to convert my clients away from windows. Its not only the holes in the OS, or the security issues but most importantly the reliability and the requirement to reboot after any installation or update creating a little downtime... Which of course is a big issue!
I am guessing you are familiar with Unix servers? And have used windows before? The commands are a little different, and the way some stuff works and needs to be installed is a little different too. Other than that it is quite similar i guess...
Transferring websites to/from a windows machine should be easy but it depends on what type of control panel you are using. If you have a plesk or cpanel on the unix server and enkompass or plesk on the windows machine it should be relatively easy to move the accounts over, otherwise it is just a matter of creating a new account with the new control panel on the windows machine and transferring all the data accordingly from the unix to the windows via FTP. The way the accounts are setup depends on your control panel. Databases depends on how you setup the windows machine. All the packages available for unix generally have an equivalent for windows even MySQL and PostgreSQL - which should make it easy to move the databases over from one to another (still depends on the control panel you are going to be using).
With a little experience of windows (OS) and Unix - it is only a matter of adapting one method to the other which you should be fine with. I think a few hours is a little ambitious but as a manner of speech I guess that yes that is all you really need.... Management is relatively easy (yet again depends on the control panel).
Recommendation of a host for a windows server is something I am not sure to be able to help with. I moved most of the servers I had in the UK to the states or other places because of the ridiculous prices here. And the speeds being very similar. Yes the ping is a little slower but the difference people see between 54ms (uk) and 150ms (us) is so small that unless you were running online games it wouldn't make a single bit of difference as long as the datacenters are well connected. I understand why you would prefer a smaller company but I guess that the bigger companies would be more reliable? NetBenefit (http://www.netbenefit.com/
) are very very good - I have used them before and they were excellent in every possible way. or RackSpace (uk) were very good too, used to have a couple of servers there and it really was good, had no downtime... But this was a while ago - so please double check for yourself and read recent reviews! Both used to have excellent service and customer care especially netbenefit!
How much you should expect to pay depends on the features you require... If you want a nice windows server running... Then in the UK you'd be looking at about £80 + per month. (whatever you will be looking at a little more expensive than a unix server. around £20+ difference)
I hope this helps!