wow so many first timers, you guys are all going to have a great time, the food in epcot is great (we tried the boxed lunches the first year they introduced them and don't rate them against the other options less than 100m away), the trading boards are great and I've always been able to make great trades in line with other attendees and only very rarely brave the back room of serious traders.
MomeRaths is right the boards are a bit of a mixed bag, if you're near the front after a board refresh generally there can be some great LE pins, one year my friend pulled the Ariel reveal/conceal AP but like everything pin trading, it really depends what you collect, I've been able to pull an AP LE from the board right before a refresh in the past (it was a tiny Chip/Dale Expedition Pins AP). In my experience if your not sure about a trade with another guest don't do it straight away, its easy to get carried away and unfortunately, there will be some people there who'll be happy to take advantage of your inexperience! Luckily, there is also lots of amazing people who won't take advantage and actually once they learn you're at your first event will go out of their way to make sure you have a good time and are able to make the trades you're looking for
As for characters, that's quite a recent edition to the event roster, last year we had Carl, Russell, Flick and Atta. At the 13 reflections of evil event the villains were actually out and about walking amongst the crowds. I don't know who we'll be seeing this year but I hope it's characters we can't usually see in the parks, like Herc and Meg. Again it's a nice add on now we don't get as many board trades as before. The other fun activity they usually run are the games on the main stage, some of them are surprisingly hard, like the trivia but still lots of fun especially once you get to know people and can cheer for your new friends whilst they compete (or have them cheer for you if you're the lucky one picked)!