I would quite like to return along the Ruhr valley, can anyone recommend any airfields along the route? Whether it be for an overnight stop or a quick refuel before making my way back across to France.
That would depend on whether you want a place with good proximity to the city to allow you to easily get to a hotel or an airfield with the possibility to camp over night. If it's the former, I'd recommend EDLH - Hamm - as this airfield is pretty much in the middle of the city of Hamm (Westfalen) - on final on 06 you fly directly over a Burger King, if that's your fancy
If you want to camp overnight, go for EDLB - Borkenberge - which have their own camping site. Both sites are in the Landegutscheinheft North so you could land there without needing to pay.....
However if you want a really nice culinary experience (albeit a little more expensive) with a nice hotel directly at the airfield, look at EDLA - Arnsberg - which is close to the scene of the Dambusters Raid on the Moehnesee - however please note that it is NOT statutory to fly along the Moehnesee humming the Dambuster's March
Arnsberg is also in the Landegutscheinheft, but this time in the South edition along with Halle/Oppin.
This is a link to the Hotel at the Airfield so that you could check availability, from a personal point of view, of all the GA airfields I've flown to, this one is probably been the nicest, the runway is also interesting, sitting on a sort of plateau with an incline when viewed from east to west. If you've got the time, money and inclination, they have IIRC a Red Wing full motion flight simulator to test yourself against 30 degree crosswinds without ruining a perfectly good pair of trousers
Based on you flying from Halle, they are all around 80 - 90 mins away (assuming Piper PA28, C172), from there to (eg) LFAT you'd need approx another 2 hours....