Anon, do you have the blacklist from previous years? I would go through the archives and try to contact the previous organizers for the blacklist. There's also a whitelist as well.
For the fields - definitely encourage people to email each other for clarification as well. I know my match and I last year emailed each other quite often to clarify and narrow down options. The general fashion type field is okay but there should also be a likes/dislike field as well where people can elaborate on their substyles or favorite characters, as well as definite "no" items, etc. Last year there was a field where you could give examples of what you would like that weren't necessarily the EXACT items you wanted to give a sense of aesthetic? This would be a great place for like dream dress lists, cosplay plan lists, past cosplay galleries, coord layouts, pinterest boards, etc. So the gifter has a general sense of the giftee's aesthetic rather than just a straight up wishlist. The gifters then could extrapolate from the info given about what to get the giftee (a wig for a certain character cosplay then have planned, an accessory to match a dream dress, a particular type of tea, etc)
Personally, sending a photo ID to a stranger on 4chan would be wildly offputting for me. Instead you should consider what the organizer did last year and verify via social media. Have them prove a history of positive feedback through at least one of the following: ebay, lacemarket, egl_feedback, cosplay.com
marketplace, LSE on FB, etc. If you want you can also ask them to provide an active social media account: facebook, twitter, tumblr, instagram, etc for cross referencing. If anyone grinches, publicly name and shame with their social media accts attached. Save their addresses on a blacklist for future organizers (don't dox them obviously) so they can cross reference to see if any grinches from past year are trying to re-enter with a new online persona/email.