As it turns out, it looks like I'll be working on any given one of those days. Sunday the 17th I'm unavailable, but as long as it's in the morning (late morning, probably, for the convenience of others), I can do it.
I've organized one of these events before (for Bastok)... It was hectic, but as long as you're willing to take charge, and others are willing to listen, it should run smoothly.
I think any damage dealer could replace the third thief. They only get Sneak Attack at level 20, so they're a bit limited compared to a lot of advanced jobs.
If you're having problems finding people, set a solid date and time, then give the occassional /sh of "Planning to do San d'Oria's Eco-Warrior on (day) at (time) (time zone)! /tell if interested in helping out/participating! [2/18 so far]" in areas of San d'Oria and Jeuno.
You'll probably get a few /tells this way, and during that make sure that the person doesn't have an Eco-Warrior from another town, or anything else that would disrupt the process on the day of the event.
Also, when I did it, I kept a list of everyone who signed up, and asked what job they would be playing. A lot of people said "Well, I can either play blm, drk, or whm", so I looked at the list and saw what we had a lack of (or, in the beginning recruitment, I said whm would be best). The list you have is very ideal, but if you're having trouble finding exactly what you need, don't fret, and consider alternate options.
If you can, bring someone on the outside who can cast Raise. The way Bastok's worked, both of the slimes AOE'd us, and over half of our alliance died (everyone who got hit by both). However, the 38 whm I recruited was able to raise them all. We went back, got their level 20 cap (after weakness wore off), examined the ???, and everyone got the item that they needed.
Hope my experience in the matter helps!
Oh, and usually there will be a few people who just don't show up. This is why keeping a list of names and jobs will help out... I /tell'd a lot of people about 30-0 minutes before the event, and a lot of them had forgotten, or didn't think we were still going through with it, or simply weren't interested anymore. I had to do some last-minute recruiting (I had everyone meet in Bastok, so I just did another /shout in Bastok, and I managed to get the extra 4 or 5 people I was missing).
Characters: Raatata, Crescia, Nyeme, Guye, Trade
I also have a Final Fantasy Tactics-inspired webcomic that I write and draw... @ http://www.landofmanyhats.com
! Enjoy! ^_^