Lookin good Mike!!!
90x60 is a pretty tight track for 1/8. A few recommendations I have:
1)Try not to pack to much into it otherwise it wont flow.
2)Pick a couple key "bigger" elements that you will build and leave put for some time and the rest of the smaller features can be more easily flattened or moved to get the layout changes you are looking for.
3)Any combo jumps or tabletops you build you should pay attention to try to make them so they "work" in both directions. Making them work both ways will really hep make your track flexible for easy changes. Heck, just driving the same track backwards really changes things.
I like your idea of an easily changeable layout. One thing that I can say is a layout does start to get boring once you have it mastered. Change is good especially if you want to keep the skillz sharp.
BTW: did I mention I am really jealous?
I wish I had room for something like that in my yard.
