Ray,
This is an ambitious project. The guilds here in the US that sponsor shows usually make their money off the raffle table and cross their fingers that enough people get rooms at the venue so the cost of the conference rooms isn't sky high. Nominal charges apply to vendors (you will probably want as many as you can get there) but they can't pay for the show unless they can expect super sales, like Sheridan (which is sponsored by the LC & SJ, not a guild). I would ask vendors for their money up front to be sure they show up. To get participants, you may have enough contacts by word of mouth, but to get attendance you're going to have to advertise somehow and a lot. Depending on attendance, I've seen guilds host shows wind up with a little extra money, break even, or go broke, depending on the organizing and the publicizing of the event. To start a show from scratch, I would ask for sponsors. Do you have a local leather guild or organization to help support your efforts?
Competitions are tricky. Assuming you get a fair amount of entries, who will do the judging? I like your ideas for catagories but for a first show you may want to make the leatherworking areas very broad. Having been a judge at many guild shows, I have been forced to compare apples to oranges, and it's better to do that then to cheapen the whole event by handing out ribbons to undeserving pieces. You might want to prepare an objective list of goals that the entry should be judged on. The IFoLG has basic rules like "edges must be finished" etc. The guild shows competitions were originally designed to help the entrants improve. To this day we try to scribe (write down) what was done well, as well as suggestions for improvement. If you try to stay with an educational or fun theme you will be safer than "Best Wallet in the UK", KWIM?
LW will of course do whatever it can to get the word out, and you can call or email me any time if I can be of use. I wish I could travel to the UK to help and attend. I would love to visit your country and meet the UK leatherworkers and suppliers.
Johanna