Welcome aboard Jimbo. I think most can echo your OP about discoveries in attics and the slight thrill this brings to a grown man! I've only one piece of advice I'd like to share if you are looking to fill 6 x 2' - please,please avoid using software to design the layout, it will look like a train set.
Grab a notepad, scribble about, work out what's a must (dockside scene, rural terminus, goods loading etc.) and when you've finished the list, go through it and delete the nonsense ones you've left in "for the craic". It's ok, we all do it!
Scribble some more on the sketchpad and when you have a rough idea, post it up here, no matter how ropey you may think it is. Based on the feedback you can tweak accordingly and then get using software to lay out the plan. I've said it before, and it warrants repeating - "lay track in haste, repent at leisure".
Looking forward to seeing your kitbashing!
Richie.