Big Ed,
Here's the thinking on the plan we developed...
1) we probably don't need a siding that's more than 12' long.
2) with the current plan, the reach to set up a train on either loop siding is about 2'. We just have to watch out for trains passing by on the outer loop. If we put the passing siding on the inside of the inside loop, we need a club member with 5' long arms to put a train on the siding.
Or, we would have to walk across the layout being careful not to step on or hit the trains on the other 3 tracks that we would need to step over.
Here's a better look at the plan:
At this point, nothing (except the wall, literally) is cast in stone!
eddiem