Really helpful, thanks for that!
I've not checked the coach on 100 or 75 track yet, there's lots of plastic seams on the chassis, bogies and wheels, so I'll see when all cleaned up how when they run - I don't really want to replace the bogies, but the wheels might be on the list...
Working with the filler, what grade of glass paper/wet-and-dry are you using?
I read earlier of your recommendation on paint stripper (Phoenix's Superstrip), I'm holding off buying until I know what paints/thinners etc I'll also need, as cost of shipping is prohibitive otherwise. If I plow straight into plastic work and filling now without stripping first, will things go bad when I come to strip later on? I'm just worried if it attacks the glue or filler.
I've got a crappy air brush (can't find my old decent one, so barely trust it for weathering let alone top coats), so I might go for Phoenix's self-fill spray can - it saves me messing up the airbrush with enamel as well I guess. I was coming round to the realisation I'd have to go for an enamel or solvent based acrylic (Tamiya etc) for most of the conversion work at some point, using acrylics just for details and weathering.
Thanks
Jon