Hi:
I agree with everyone else that you've got a super first go at painting a background. The layering reminds me a little of the Virginia artist Victor Huggins' work. Don't know if you can find pictures of his stuff on line but you might like it. Beautiful renderings of the Shennandoah valley area.
A couple of other techniques i've seen used, but haven't yet tried; Keep a space between your actual scenery and the background- this helps create a feeling of distance. Mirrors can be useful to increase depth of field- the best uses i've seen have been in limited areas, a "hollow" in the mountains, a continuing industrial facility or warehouse district, etc.
Keep up the great work! I don't have a permanent layout of my own so i live vicariously through all of you.
Regards,
Ted