It is always useful to look at layout plans and exhibition layouts to get an idea of what works well. You need to sketch out a few ideas and see if they fit your space. Keep the radius of curves as large as you can. Whatever you start setting up it will change as you start running trains and see the shortcomongs. It never works first time around and don't jump in with a complex design.
There are some simple ideas here:
http://www.bandrmodelrailways.co.uk/Design%20ideas.html
Probably not his fault but the way Ebay is set up, however he wants £20 to post to Ireland but only £12 to the UK! He even offers free collection for UK but not for Ireland
There have been several Bachmann Mk2As on ebay recently and they all reached good prices compared to the original selling price.
http://www.ebay.ie/itm/Murphy-Models-Bachmann-4110-Mark-2A-TSO-Open-Second-Coach-IE-Intercity-X-Two-/261170777802?pt=UK_Trains_Railway_Models&hash=item3ccefdceca
Not to worry, Brian, I ubderstand that you are constrained by Corgi's requirements. It would not be too difficult to change the model's identity after I buy it.
I think changing a casting from dual to single door would be more than just a commission. I wasn't aware that Corgi do commissioned models so does that leave the new Northcord model of the EV?