Hi Colin and welcome to the world of M3Ws!
There are already a few of these in France and I'm sure they wil be along to say Hi shortly.
The immobiliser is easy to check - if it has one it won't start without waving the tag past the ignition switch. In the UK it doesn't seem to affect the insurance anyway.
€350 is in the right ballpark, mine is just over £300.
No need for a helmet in France (nor many other EU countries inc UK).
I'll defer to the locsls re numberplste snd MOT.
Chris