Nice pictures. I like the looks of the little Roundhouse locomotives when they have a tender. I built a William tender and added it to my Billy. I originally had a coal load like yours, but added a railing to the tender and changed it to a wood load.
I made my own drag beam out of a link so the tender pin works for easy coupling, the drag beam swivels and the tender is close. If you decide to couple your tender closer, you will restrict how tight a radius the loco and tender can make. Mine is so close that I cannot take less than an 8' radius. Minimum radius on my layout is 10 feet.
I also changed the buffer beams to wood, added working headlights (battery under cab floor), added a Regner single chime Euro style whistle and added R/C for the throttle, reverser and whistle. Servos and receiver are in the cab and the batteries are in the tender.
everything is scratchbuilt except for the little four-window coach next to the tender, which is from twin mountain models. i believe they are offered by ozark now? the buffer couplers come from www.grsuk.com.
i really don't know that scale has any meaning at all to me in the garden context, so there is no scale and no prototype. i just eyeballed everything the match the roundhouse locomotive. most of the cars are four-wheeled, while the long coaches ride on some awesome little accucraft trucks (maybe intended for gondolas?).
The flat behind the tender and the water car in the distance are scratch built in 7/8n2 scale (1:13.7) and are for my live steam tram to pull. Normally I pull four LGB 4-wheel passenger coaches (2 are compartment cars) behind the Billy.