The key is to use the right buildings - I'm pretty much using the Ratio range as they are classic GWR. If your signal box is the right colour it will be a big help for a start. Station architecture varies a lot but things like fencing and valances can make a big difference. You could use a resin staion, rip the old valances off and replace with the correct plastic ones for example.
Era? Well start with road vehicles. No need for acres of cars, most people could only dream of owning one in LMS times. Plenty of horse power though, the sort that eats from a nosebag. Three wheel delivery vans based on motorcycles (Oxford diecast) were popular in large towns and cities.
The list for this is huge and comes back to careful examination of pictures from the time and location. I'm sure others will be able to fill in more details though.
You are bang on though when you say, "for a first attempt to get soemthing to run on, anything is better than nothing". You are very unlikely to build your perfect layout first time. Far better to build a testbed layout to get the hang of all the techniques and make all the mistakes. By thinking of it as a testbed you give yourself permission to give things a go accepting that they might not work. Once you've built the model, the dream layout will happen far quicker because of all your new skills. Mind you, we built Flockburgh as a testbed and liked it so much the dream layout never happened.