Regardless of what others have said this is what I strongly feel you should do:
Crossing the Channel is a very easy cruise in the summer, but can be hard work when doing it for the first time and when it gets rough.
Before you go, get yourself on a VHF course, go and do a powerboat 2, and get familiar with how your navigation kit works. Also take spares, even though your boat may be new or Navigation equipment new, always carry a chart and compass, this way if you have a bearing and your GPS goes down for whatever reason you have a heading to follow. Carry a handheld VHF, as mobile phones sometimes dont work in the middle of the channel on some networks.
Make sure your lifejackets have good gas bottles in them etc, and all your kit is in working order, carry more fuelou need, just in case. If you repect the water and plan properly like this you will have a great time, by doing the courses also , this will give you great training not only for the channel crossing but any boating you may do, in your pride and joy.
Remeber you are resonable for the people onboard while you are at the helm, by making sure you have done all these things, you show no neglict or leave things to "luck", one last thing-inform the coastguard of you movements, expected ETA etc, this way if something happens they are there to look after you. Just dont forget to let them know you have arrived safely!!
Re ETEC, I took the Thunderbolt over to Guernsey from Portsmouth in the Summer. I used a total of 120 Litres going over at about 3500-4000 rpm. This was when the engine was brand new, it also used alot of oil, 3litres! Having said this, the engine had not been really run in and on the way back, drank no oil whatsoever, still though drinking 105litres of petrol. So take some oil as well. 5 litres will be more than enough.