Andy,
As they say, there are no dumb questions, only dumb answers .... so here's mine. Transiting Cambrai's airspace isn't a problem, you just may have to avoid the overhead. I transited through about two years ago from Beauvais to Maastricht at 3500 if memory serves me right. What routing are you planning to follow? I would have thought a route Lille Florennes Luxembourg would be more direct. As for Luxembourg itself, great city for a break but the airport was a bit of a bind the last time I was there. In any case, enjoy your self and let me know if there's anything other info you require.