All I'm worried about is, operating (potentially) across Europe, IFR in an N reg twin, with an FAA PPL (but no FAA IR or MEP), and EASA (UK issued) CPL\IR\MEP, based in France, am I legal?
It seems like you need to get your faa mel and faa ir ... At present you are only alloud to fly in the UK in imc and or mel. You can do all that in europe by the way. Should not take you very long.
Do not believe the jokers who say their easa license will be sufficient in any easaland. Albeit they call it the land of the free, americans are very much by the rules. The rule says foreign state .. And easa is not a state .. Pure and simple., so your uklicense covers you .. But only in the uk.
As far as france and faa is concerned. a couple of people high up in the french caa have an n reg and realise very well the benefits of the. Faa system. This is also the reason why the french went ahead and made a french ir rating which they will continu to recognise in france (this was the only place w ere it was valid anyway).
They fought very actively to get a couple of things through with the cbm ir.
So no worries about n reg in france. However you will need your easa license as well.
You will be rampchecked sooner or later .. This is mainly for vatreasons. Once you are in the clear on that they will log it in their database and you will not be bothered anymore.
On this issue I had a funny encounter as well. I am based in rotterdam which is a customs airport and on a nice day i filed and flew to Den Helder. I was straight away ramp checked by 2 guys who were send specifically from the amsterdam office (1.5 hours away). Why they never checked me in Rotterdam but did decide to do it on this occasion I have no idea.