You're best bet is to try some combinations of characters you have the most stuff for, and find a team that works well together.
Looking at your crew, I recommend holding ramza either way, because his EX makes him incredibly well rounded!
I'd probably go with Ramza, Terra and Cloud right now, and replace cloud for Celes once she gets a few levels in cycle quests.
Since they kept a random element to the quests, where a monster can show up in the final wave that mulitply's most rewards by 10, it's a good place to level grind with EXP books! And Gil books if you do the money one!
I recommend building up Laguna as soon as possible since you already have his 35CP, since that's literally the only luck-requiring part of his kit you need to make him the amazing all-rounder he is. He buffs everyone's MAXBRV, lowers a bunch of enemy stats, and provides battery and dumps into HP damage, he's Amazing. He'll be a huge help in regular quests and cycle.
Don't waste power stones on anything but leveling EX weapons if you can help it, the passives you get on those are absolutely worth spending power spheres on, at least with characters you want to use, and copies should be saved for way later down the line, if you're lucky enough to get some.
Outside of that, don't be afraid to just load up on the current Co-op event/s on Just For Fun with you're favorite powerful characters! Not only is it fun to try out different units with unusual team combos, but it adds more tension to the experience, and gives you better info on how certain characters can be effective that you wouldn't know by yourself.
I kick all sorts of butt with Fujin, since she both adds wind weaknesses, and empowers everyone's neutral/wind attacks to do more damage to wind weak enemies! It's a blast when it comes together!
Plus, all that fun also pays out in tons of tokens, that you can use to shore up a character's crystals, or build up reserves of fusion material!
I will warn you though, currently the Co-op event is kinda rough to play without an effective character, but when Fang rolls around you can use whatever, and it'll be just fine!
I hope you end up having a ton of fun with the Fang event! Search the thread a little for my and the others' friend codes if you need help in Co-op or want a mutual follow!
