I do not have any experience organising wood turning shows, but I have attending a few wood related events and I have organised fan based conventions. Off the top of my head these are teh things I would seriously thing about:
Advertising: If no one knows it is there they will not come (no matter what Kevin Costner says). Advertise online; at turning clubs and shops (do not restrict it to just the local ones, people will frequently travel over 100 miles to get to this sort of thing). Put up signs on major roads nearby to catch passers by (A4/A5 does not cut it, you need A0 signs or you can not read it at 30MPH), be warned there are restrictions on how close to junctions you are allowed to post signs these days. In your advertising make it clear there is no door fee.
Directions: when attending anything of a decent size I expect to see Yellow AA signs, or at least A4/A3 hand done signs out to the major road junctions. If done properly this can also act as partial advertising. The last time we did it was about 10 years ago, but we paid £300 for AA signs put up al over Manchester. If you are not charging an entry fee this may be difficult to justify.
Space: There is a fine line between too much space that makes the whole place feel empty and under utilised; and everything so crammed together that you have to push past people to get anywhere. Yandles is about as close together as you want people to get.
Parking: One of the reenactors markets almost failed on the first year because the exhibition space had everone parking on grass... In October... People needed to be pulled out by tractor. ensure that you have sufficient parking for all of the exhibitors (they will be bringing vans) and all of the public. If you are in a city centre then you can make use of NCP car parks, otherwise you may find that try to find a parking space, fail and then leave.
Food: If you are not in a city centre then you will need to make sure that there is enough food to keep people in the building, otherwise they will leave as soon as they get hungry. I have never found a venue that has sufficient internal catering to accomodate a large number of attendees who all want lunch between 12 and 2. You might not have a choice depending on your venue (they may insist that they do all of the catering), if you can get external caterers then a burger van, or saugage in a bun, or a hot potatoe van are welcome sights to hungry punters.
Tea and Coffee: People always want easy access to drinks, external vans are easiest from your point of view as they are geared up to dealing with people quickly. If you are having guest presenters then you will make them happy by providing them with food and drinks throughout the day.
Quiet areas: People are going to want a quiet place to sit and have a natter with their friends. They are also going to want to have somewhere to mull over potential purchases without being in peoples way.
Overnight: You mention that it is 2 days, what are the security arrangements for overnight. the exhibitors and traders will have a lot of stock (and hopefully a lot of money (let them know where the banks are so they can deposit day one's takings early). what are the sleeping arrangements, are you putting people up in B&B, or are they making their own arrangements.
Set up and take down: Have you allowed sufficient time for the traders to set up before the start of the first day (it will take longer than you think, especially if they are all bringing stock in through the same door). do they need to up turn up the day before (if you are opening at 9am on Saturday then they will need to start setting up at about 6am).
Toilets: Most places do not have enough, think abotu portaloos. Get them cleaned regularly, there si nothing worse than going into a loo and there being no paper or a blockage (this applies to both site and portable toilets.
