Mike Price
Hello there!
Not being a GWR follower myself I can’t really advise on what kits you would need. Whatever you choose, any kit can be ‘converted’ by just substituting an EM wheel set available from the Trade Officer.
There are numerous coupling systems; all (dare I say it) require some work on the wagon usually at the time of building. I personally use ‘Sprat & Winkle’ but where I have a fixed rake of wagons I use three link couplings with a S&W at each end for changing the loco and brake van although some people go the ‘hair shirt’ route and use 3 link throughout!
Hope this helps,
Mike Price