So is 'the quarry' to enable the High **** ironstone branch to be modelled? There's a proper use for the O2s we are expecting from Heljan fairly shortly. Lucky man, you can also run the 'Aldwarke job' from High ****, the UK's only scheduled fully fitted express mineral train booked for a pacific, usually a Pepp A1 or a Gresley A3.
I will echo the advice on curve radius already given. I determined by experiment that for full size ECML trains to operate truly reliably I needed a 30" minimum radius curve, and the Peco medium or large radius points in all the running lines. If scale speed running is observed, even the DCC system tripping out will not cause derailment of any trains that happen to be on a curve. That becomes rather important on an extensive layout, you don't want to spend half an hour finding all the derailed vehicles after a DCC system trip.
Another aspect that I suggest needs to be reconsidered: it looks like your fiddle yards require 'duck under' accesses in order to reach them. How can I put this, duck unders very quickly become very tiresome. You have the length of run to make very slight gradients possible, the ECML's ruling gradient of 1 in 200 is quite possible. Model railway barely notices such a gradient (in fact many 'level' layouts will be found to have such gradients on them) yet with some careful planning these could enable you to have the fiddle yards underneath the layout as already suggested: try for below the front edges of the scenic sections.
I recommend the Kadee coupler for reliable auto uncoupling operation. Neat gesture toward something prototypical in appearance for the ECML, as the GNR started using the knuckle coupler from 1895.
And finally, do some careful thinking about the number and size of trains you will want to operate. Your plan shows what I estimate at roughly 80m of off scene storage in the fiddle yards.
My ECML operation covers the KX inner suburban area, and is similarly on the plan of all trains which go North eventually return going South. To make a decent stab at a full representation of the scheduled traffic I have a planned 32 train formation slots, and eventually 110 locos* to operate these; the operation starts out all steam, and moves forward in time through the diesel transition until the Brush type 4 appears (then it is reset to all-steam and starts again.) I don't take locos and stock off track but shunt them, as experience has proved this is the way to minimum damage and trouble; this matters when you have a large operation to maintain. That requires about 120 metres of off scene storage track, and there always needs to be a through road kept clear in any fiddle or sorting yard to enable both the traffic to flow and shunting to be performed.
(*In case anyone is curious, now at roughly 90% of plan, and mostly from RTR produced in the last 15 years. Shy a few steam loco classes, all of them relative 'rarities', the biggest gaps an A2/3, K2, J19, B16 and N5; need more ex-GNR design coaching stock, and the wagon stock needs significant augmenting with LMS design wagons to supplement my existing kit builds. I got lazy there, reasoning that Bachmann surely must 'press-on' and offer LMS designs in matching quality to their LNER opens and vans. But this looks increasingly unlikely.)
.
