After a great deal of thought I've finally decided on a track plan for the fiddle yard - well the main bits anyway. There will be five storage sidings to the side of each of the up and down main running lines which will run through the middle of the sidings. The sixth track will be a run around loop for locos etc. This also has a pair of turnouts for additional storage into the four corners in order to maximize use of the space available. I am considering putting one or more loco turntables in the corners next to the wall.
Having finally "mastered" Templot - well sufficient to produce the plans in the attached photos - the entrance/exit at each end is via a pair of C12 scissor crossovers. These are on a 1600mm curve and are at 50mm centres. I went for the C12 as the minimum radius on the inner crossover is 44.4". The use of the scissors will give maximum flexibility.
Gluing the printed A4 sheets together was an interesting exercise!