UK train trip..sounds pretty sweet...some of the hubs you might wanna try are
London to Birmingham
Birmingham to Manchester
Manchester to York
York to Edinburgh ( YEHA)
Save your pass and bus it to Aberdeen ( trek north into the Highlands)
You could then make your way down the western coast and eventually into Wales.
The one thing you do seem to have on your side is TIME, which will be your biggest advantage.
I can make all suggestions you want, but remember, this is your trip, so use what advise people give you and mold it into your own adventure...