Ok. To go with Ace's excellent recommendation to have time out to think, I have the following updates.
I've tried negotiating some more space, but to no avail.
So here is the final design brief:
-5 x 3 max.
-Need to have two levels, preferable separate levels, one for electric (lower level) and one for clockwork.
-It would be nice to have the lower layout to sit down to, and have the upper layout as low as possible (I use a cane and have somewhat limited mobility). In a perfect world I could use a standard chair to sit at to use the lower layout, and a high bar stool to use the uppermost.
-Simple to construct, as I am not much of a carpenter.
-Use castors to allow 360 access. This will also keep the wife happy.
-Storage space would be nice, but not a necessity.
The lower baseboard would be good to have at 24" from the floor, then the second baseboard at 48". This way my legs will fit (just) under the lower layout, and hopefully the stool will allow me to access the top baseboard with moderate ease.
Of course the layout designs will feature most switches etc at the front where I can reach them, and a simple run around track at the rear. I have both layout designs (one heavily inspired by Bluesheepbrian's superb ideas) done to my satisfaction.
I am not running large loco's, the largest being an Ives 1694, and have setup both layouts and everything runs as I want it to.
So the big question now remains as to how to build the supporting structure for these baseboards. Do I try to take the easy way out and go with industrial shelving? Light weight and easily height adjustable, use of shelf stays, large weight bearing capacity etc. but at the expense of looks.
Do I try to build a wood structure to make an attempt at making the unit more homely?
Again, comments most welcome!