steve - welcome.
Have you been across the channel before in any boat? Mid Channel is not somewhere I would fancy in an inflatable Kayak. If you were lucky with the weather and good with your planning it could be OK - although other than to say you had done it I can't see why.
Nos may be right but the French are a bit funny with their rules. They basically see crazy brits crossing the channel as a liability and may not be keen to encourage it. You might want to read this for some of the challenges involved:
In The Bath: Conquering the Channel in a Piece of Plumbing - by Tim FitzHigham
Oh and in terms of support boat I would suggest there are a couple of criteria:
(1) Shelter. The poor bugger is going to be sitting there for a long time and if you need 'rescued' somewhere to shelter is going to be important.
(2) Happy at low speed. In theory any RIB will tick over all day long - but doing a few knots can be hard work and very fuel inefficient in some ribs.
(3) Have a reasonable turn of speed if required - either to get ashore for help or just if the weather means an abandoned attempt - you want to get home in a couple of hours.
(4) Have reliable engines / twins / good aux etc. You don't want to have to abandon an attempt 3/4 of the way because the engine is dodgy.
(5) Be flexible enough to go on the best day for you.
(6) Not be too smelly / fumey. If you are sitting downwind from it you don't want black smoke or 2 stroke wafting over you all day.
(7) Should seriously consider AIS and/or Radar.
Finally, if I was going to paddle it I would have thought some very good sea kayaks and appropriate safety kit, training etc would be a better investment that a support boat.