We'll decide on roles and such when we finalize who's going to be participating. There's going to be a strong need to focus in specific skills though, so roles will be very helpful. For example, warriors are probably the easiest, but unless you have 70+ smithing you're not going to be able to get adamant equips. If someone is dedicated to only smithing, they should be able to make a number of mithril equipment parts within a reasonable amount of training time.
As for mages, the highest battle spells you'll be able to use are the ones powered by mind runes, unless we get some people to farm monsters for chaos rune drops (probably easier than farming things for death rune drops). Archers will be even harder: I'm not sure what drops bows, but Minotaurs drop a very high amount of iron arrows, so those could be relied on should someone find a bow. We can (should) have more than one of each role though.