The purpose of the cork is simply to lift the track up, some. Your ballast materials will fill in where it is needed. Like Willie said you could use N scale for Arrival/Departure and sidings and then maybe HO scale Cork for the rest. Your yard should be flat, no cork. Yes, retaining walls were used by the full scale in developed locations like cities/towns; or, where they were absolutely necessary. However, I think they where far less prevalent than as seen on many Model Railroads. Like all of us, I would assume CSXGandn wants to save some money where he can on his layout. Buying retaining wall materials for the length of his elevated track could be costly. Apparently, none of his track work is permanent at this point; so, why not give himself some room and make the slope between the elevated track and lower track more realistic. He could even narrow down the track bed on the elevated road bed to help with this matter, start the slope by lopping of some of the extra width of the woodland scenics risers.
I believe I might be overstepping my bounds by making these suggestions! If this is the case, I certainly will back off! This is a hobby where artistic expression should be first and foremost. CSXGandn please do what you want/like and pay no attention to what others suggest, if you like!
You're not overstepping your bounds at all! If I didn't want to get a lot of different suggestions and input I wouldn't have asked
As a matter of fact I spent much of last night messin' with my track plan to see how I could improve it based on suggestions from this thread.
Not only is there a cost with all that retaining wall, the track has to come back down on the other side. That's a lot of retaining wall! It probably wouldn't look good.
So far I've managed to get at least the lower tracks nearest the highest elevations moved away. That has created some better staging scenarios! (staging will be hidden under the 7' long elevated section).
Thanks, all for your suggestions. Feel free to keep them comin'! I will post more pics and/or vids as I bring it together.