Best of British mate, nice idea but hope you realise that's a hellava lot to take on! Don't want to pi … sorry, rain on your parade, but have you thought about all the public liability insurance/risk assessments/tickets/security/etc. you'll need to stage such an event. Unfortunately nowadays you need all this and more, not even because of the Council/Health & Safety Executive officials that are forever skulking around in the shadows and if your paperwork is not up to scratch can slap an injunction on the event minutes before you open the gate, but because of the public themselves. One minute they are placid fellow off-road enthusiasts just like you or me, the next they are raging nutters who will sue the pants off you because one of their number has been hit on the bonce by a 5 mph sign that became airborne. Rather you than me. Been there, got the t-shirt and video - usually because I bought or commissioned them in the first place!
My advice? Better to let someone else take the risks and instead do some simple fund-raising as a punter. On the other hand, if there's a lot of you one can spread the load both logistically and if the smelly stuff hits the fan. In other words, don't leave yourself vulnerable coz you could easily end up as the scapegoat and in financial terms, could quite literally be 'paying for it for years'. As the late great Brian Clough would say, ["b]Think on young man, think on".[/b] He was from your part of the world and was no mug; heed his words wisely Kieran!