To actually answer your question, instead of spouting more drivel than necessary, I have a few recommendations;
Much of your tasting is obviously going to be reliant on the wineries you are representing. You have indicated the number of guests you want to serve, but not the number of wines being poured. That is a huge factor. I have arranged tastings of as little as six wines for a hundred people and tastings of as many as 200 wines for 2,000 people. Logistics is the key.
The number of wines poured will determine if you want to arrange a more intimate, sit-down tasting or a larger tasting where your guests roam from table to table. Will you have representatives from the wineries there to discuss the wine? What is the purpose of the tasting (to educate on the specific wine or more as a social gathering)? If full education is the key, than I would recommend keeping the tastings smaller and more frequent. There is nothing worse than trying to learn about four dozen wines in two hours when doing one dozen for one hour once a week for a month would have been more instructional.
Water. Spit buckets. Note pads. GOOD glasses. White table cloths (to look at the wine). Bright, natural lighting (can't tell you how many tastings I've been to with "mood" lighting). Pads to take notes. Information on the wine (not the PR stuff as much as the production information).
I hope this opens more questions about setting up a tasting -- vs. the pithy comments that seem to abound on this site...