Hi Dennis,
I believe the training sessions in Dover Harbour don't start until May, but you might want to double check that with the CS&PF or the CSA, they might also be able to tell you about any other groups that swim this time of year.
http://cspf.co.uk
http://www.channelswimmingassociation.com
For accommodation, take a look at
http://www.stayindover.co.uk/accommodation, there's a range of options and prices.