Well the last design wasnt working for me as I had no room to extend. I have therefore decided to go for a two sided layout on four 3'x 15" boards (layout attached).

The board with the crossover will have a hill/Tunnel arrangement over it and control equipment inside the curve/railer on the siding.

I am still with the Kato unitrack because I have to much to get rid of - I did carefully consider it this time as it does lead to a larger curve radius requirement than other track types.