Take some spare fuel cans with you - petrol is far cheaper than mainland UK.
I found the journey to be a piece of cake - mind you the conditions were great and the boat is a 9m but considering I had never been on the boat before it went very well. Couldn't have done it without my trusty Raymarine though!!!
Check this before you leave - you can see EXACTLY what conditions you will face mid channel.
Be warned it is a lot colder out there than you would think - Guernsey and the mainland were sweltering - about 26C but mid channel is was down to 12C = good job I had a ski mask.