Our personal main team is Earth/Light/Air and it works very well for us, actually.

However, we have used Shadow/Light/Air, which, so far as I'm aware, is a pretty common combo

Air element is best statted in str and dex, because its debuff bleeding depends on crits (and BOY does the damage stack up)

Depending. Shadow tanks can probably go with several variations- our own is 2int/2agi, for damage output to get higher heal return from debuffs, and greater evasiveness and defence (but he's a max stat and has an Ancient Lightbringer Relic, which may be skewing our views of effectiveness)

Lights are mostly just the healer element. Stat them first to int, probably. Secondarily you might want to go for dex because crits would get better heal return (People often equip healer light pets with Evoker/Pyromancer equips, for Int/Dex, I think? rather than Illusionist/Lightbringer (Int/Agi))
(our own two are set up gear-wise so they can at least hope to tank a few hits if necessary if our Tank gets KO'd)



(To cover Earth where Savynn didn't, they make a pretty dang good tank once you get a handle on them.
Their ability to force opponents to focus on them is a pain earlier on, but combined with Thorncoat (lv30 ability), a str proficiency point, and a Light element healer on hand, it means you can basically force an opponent to punch themself in the face at little cost to yourself.
Also handy if the opponent is charging for some big attack- force them to go for the tank and the other pets are left free to attack rather than block.
Ours has been primarily statted in Str/Agi.)

Thanks!