Sorry to hear about your Dad. I hope he is recovering well.
How much financial support do you think is needed for the event? When
you say it would be hosted by your department, does that mean the
department needs to be paid for that? Wiki Wednesday's in London are
having a difficult time finding sponsors or venues, so it might not be
easy, though there are at least a couple of Wikimania sponsors with
people in the UK, so they might be companies to consider asking for
support. The Foundation, Wikimedia UK, or possibly even another
chapter in Europe, might also be able to provide some support.
If by big names, they mean speakers, then you should contact Jimmy and
see when he is free and in Europe and set the date for when he can
attend. Perhaps they'd count people like Alison Wheeler (chair of
Wikimedia UK) as a big name as well?
I also suggest you get Cormac Lawler involved. I think he's based in
Ireland. He's a researcher and has been involved with Wikimania and
would be a good fit for this, both as a speaker and organizer.
Angela