I think the issue you have here though is the fact that most new students will be new to flying, no experience or knowledge in the field whatsoever and therefore there first few lessons are usually spent deciding whether flying is defiantly for them or not and if they can stomach it and adapt to 'driving' on 3 axis! I can only assume that this on its own is quite hard on the brain for some at first and then if you throw things like W&B, MTOWs, Fuel consumption calculations etc in from day one then i think that could be enough to cause brain overload for some and really put a student off! I know that on my first lesson i certainly was not thinking much more than 'am i gonna get back on the ground alive'! After all, the idea is to study for the ground exams parallel to training in the air, so your coursework is relevant to the exercises you are doing in the air, hence why W&B and fuel are not usually thrown into the equation until your due your solo navigation exercises as this is when you must have the Nav exam done and passed by.
As for training overweight in the cessna 152, like others have mentioned, i think this is a practise that is used more often than not and i think to tell a student that he has to train in a 172 is not always going to be the best idea neither. I know i could not afford 45 hours in a 172 for starters! and if i was told i could not fly dual in a 152, then i would find another instructor who could! Im pretty sure i read on here somewhere that the 152's MTOW actually has quite a large safety margin and altho i would never even consider loading to that margin, i do trust my instructors opinion as to what weight he is willing to take! After all, my instructor has had an ATPL since the 1970's and has much over 10k hours experience split between medium/heavy jets and light training aircraft and more importantly, he is still alive!
Tay -Yak sounds like a brill idea! if only i knew of a place local that owns one for hire hmmm lol.
Anyway, with regard to the le'touquet trip, i will complete my PPL, im going to gain some hours experience doing local flights with friends and i shall more than likely get a NR out of the way. Then ill do the cross channel check ride and make my mind up from there.