Firstly on the unpainted army front, I don't think that I have
ever fielded a completely finished, based and fully painted army at an event, hence my 'Black Legion' EIR army. You see a sense of humour and a penchant for puns is a prerequisite for a wargamer IMHO...

As to non-GW figures. Well that's a tough one, I don't know what the general policy on that is in WHW, as effectively its just Tom booking a load of tables for him and his mates, the mates of course being us... When I ran the Euro GT they had a 'you're paying, so its up to you' approach, but these sort of things do have a habit of changing pretty frequently... It's probably best to ask Tom directly...
As to additional lists, err... Just make sure that you explain everything before playing, and where possible publicise the fact that you're going to be bringing a 'non-standard' list prior to the event. I've taken playtest Norse lists to use at events before, which does of course give your opponent a handy excuse when you beat them

Also bring plenty of print outs with you, I know for a fact that I won't have the time to fully read through every variant list that is out there now, heck I was even caught out by the latest 'official' Lizardmen list at the August get together at the Civil Service Club in London, which was also a pleasant one day affair.
So, onto more important matters. Is anyone considering staying in Nottingham the night before or the night after? Admittedly I can probably blag a bed in a spare room of a family friend, so won't necessarily have to fork out for a hotel room. But there are some very good pubs worth visiting in Nottingham, and for that matter a few good places to get a curry. And I for one more than welcome the opportunity to spend an evening getting sozzled and talking about toy soldiers, etc...