First off, thanks to Ian and Tamsin for your responses to the varnish question. I just used Matt varnish rather than gloss then matt. Also thanks to Doug whose comment on using lighter colours on 6mm. When I looked at the figures from a reasonable distance they did just merge into a dark blob, so I spent some time adding fresh highlights to the greatcoats to make them lighter and stand out more.
I have also completed my first base over the past couple of evenings. I decided to complete one base initially as I wanted to play with different colours, etc. until I got a result I was happy with. I also learned that its not a good idea to place the strips so close that you can't get a brush between them to highlight the gravel or add flock. I also added gravel to the entire base before I had glued the skirmishers on, this caused me a number of problems getting them to look right. In the end I did the best I could and then used more static grass than I planned to cover up the messy basework. I'll use less grass on the next base.
I initially went for a muddy brown winter effect on the groundwork and grass, however, this with the brown greatcoats just looked like a fifty shades of brown homage. So in the end I went for a brighter effect which I'm much happier with. The grass was too green for my liking though so I drybrushed it with green ochre to give it a more autumnal/winter look.
So pictures of my first base completed below, I'll continue doing the bases one at a time for the moment until I'm completely happy with them and will add more pictures as each is completed.
Once again, thanks for all the comments and tips. I really do appreciate them.