I think that's personal preference. I like 4 man better than 5 man, but sometime you really need the MP rape or the portals. Eni/Iop/Panda should be core though.
As for element that's personal preference too.
Iop probably strength because of wrath, or strength/int with sword of fate.
Eni I'd say int is nice for heals, agi/cha seems more pvp oriented.
Elio either agi or int, but then again i don't know.
Enu chance is nice I'd go with chance for Pvm.
Panda anything works. I'm a big fan of int panda but mine is chance