I think you have made a great start, well done. These sorts of models can be excellent. I have bought several old triang mk1s and replaced buffers, added gangway ends, new wheels, reglazed and painted inside and out and I am pleased. Looking at your pics I would say the best thing you can do is some simple weathering on the undeframe. Coaches were normally kept clean so no need to go mad, but some track colour lightly sprayed over the lower half would add a lot.
Well done.