Really appreciate your comments guys, expert or not! ... and Dave, your idea of a bit more 'overall' weathering on 68901 will probably do the trick for me. Cheers for that.
As I'm not doing very many, (budget constraints!) I've stuck with the same approach/technique to give the rake a certain 'togetherness'... so there's two 'personal preferences' straight away! Maybe I'll try another technique for an 'on it's last legs' wagon left to rot, all alone, in the yard!
Re the coal loads, Dave (all 'real' and sitting on easily removable see-saw bases), for variety I've done different piles/sizes in other grey wagons, but I also wanted a consistent little group comprised of wagons that had obviously been filled in the same way (two drops, I suppose you'd call it). 'Tis based on a photo of a long coal train in Wales (bird's eye view) which I thought was very appealing. All destined for the local gas works, maybe.