Fred,
You are very close. WS makes Scenic Ridge, but that is a full-fledged layout, 3'x6'.
What you guys need is the WS Sub-Terrain Scenery Kit, 12"x24" #785-929. This kit comes complete with everything you need to build a diorama and practice your skills. Look on page #174 of the Walthers N scale cat. $49.98. Check ebay too. Someone may be selling the kit.
Marc, and all of you,
If you start something big and mess it up, just tear it out and do it over again. I can't tell you how many times I have ripped up perfectly laid track because it just didn't give me enough room to put that prize winning model in place. Or tear down the mountain because I really needed more yard space. Or repaint that prized model I mentioned because the colors did not look right from the bench to the layout with different lighting. Or start my third layout in the same space within 4 years because I changed scales.
In other words, try your best. Only you can be the best judge of what is right for you. There are a thousand techniques for doing the same thing. Try one at a time. Do not be over-whelmed by the task ahead. Focus on one task at a time. There is no right or wrong in this hobby. It is all just opinion and what feels comfortable to you for what your ever changing goals in this hobby are. Remember this. Most model railroads are never, repeat, never finished. If you do not like something, tear it out. Now you have learned something new, you don't like the way you did it. Try another way.
Life and this hobby are a learning experience. Enjoy it all you can while you can and be proud of what ever you have accomplished. That first craftsman kit you built, the first mile of track you laid or the first time you tried water (Marc get off the dime!), no matter what it looked like, you did it and should be proud. Not satisfied? Go and practice a new technique. This is not a science folks. It is a hobby, a pastime a leisure activity. This is for your pleasure and I surely love it!
To really answer Marc's question, it depends. In the beginning I built dioramas. Now I just zoom ahead. Don't like it, tear it out. Frankly it just doesn't hurt anymore. And actually for this layout, I have no written plan. It is all in my head and I'm sure there will be a hundred changes to it before all the track is laid let alone the scenery. That is the subject for another discussion.
Now go ahead and paint, plant, weather and make water (since my operation I seem to do that a lot.....there I said it for Marc). Frary is the master. WS practice kit.
Enough or too much said.
Fearless Leader, Pete