I've never done a large group brew, but I have gotten together with a couple buddies to split a big batch. it's fun to have some company on brew day, and it makes cleaning super fast and easy when you have many hands to do it. we typically pick a new recipe that we've all been wanting to try, and often will structure it so we can each do a slight variation on the beer for later comparison (different yeast, dry hops, fruiting, etc). way easier than brewing several batches on your own to compare ingredients.
as far as traveling with wort, it's not an issue. make sure you follow good sanitation practices, and I wouldn't go more than 24 hours after chilling before pitching yeast to avoid any chance of infection. you can also pitch yeast once the wort is knocked down and travel with that, it's not going to hurt anything for it to be sloshing around a little. just make sure you're not in super-active fermentation where there's a danger of it blowing off all over your car (almost happened to a friend of mine last time because he left the day after we brewed). typically for group brews there's some sort of brewmaster who's running the show. check with them about what equipment you should bring (mash tun, kettle/burner, chiller, hose/splitter, folding table, camp chairs, cooler), any ingredients they need (don't forget water chemistry), and what you're doing about yeast. definitely bring some homebrew to share.
