mimgrim
Smash Hero
Well, I currently have Riki with Hero Time, Happy Happy, You Can Do It, Tantrum, Bitey Bitey, Lurgy, Freezinate, and Burninate. I just pretty much let him do his thing and stuff works out lol and he helps to keep aggro away from Melia.Sharla can be fun late/end game when you can put out Thunder Bullets super quickly that do thousands of damage.
Not super sure about Riki (I typically focus on ether arts personally but he's got some interesting tools), but Dunban I find can be built one of two ways. You either control him and make him an agility tank or you use Heat Haze and go all out offensive while someone else tanks. The only thing that changes with certainty is your choice of stances in this regard. Evasion tank Dunban goes well with Serene Heart and either Peerless or Jaws of Death (depends on whether you want to shorten a fight overall or have some protection). I would say that Gale Slash, Worldly Slash, and Tempest Strike are all givens regardless of build. Thunder is fun for goofy Chain Attack setups and can near-guarantee smash an Arts tag if you want to forcibly stop an enemy. Electric Gutbuster and Steel Strike grant Dunban a solo Topple setup, but the long cooldown on SS has me preferring other arts. Final Flicker is an awesome way to get Blossom Dance back up faster if you're not worried about HP. I ignore Demon Slayer as the cooldown is quite long and a bit situational. Battle Eye is great in single-target fights and stacks well when gemming/linking for Double Attack (like the skill link that turns all DA's into criticals).
Dunban has Spirit Breath, Serene Heart, Peerless, Thunder, Gale Slash, Tempest Kick, Worldly Slash, and Blinding Blossom. I really can't decide if I should give him Heat Haze or not, I don't control him or anything (because there is no way in hell I'm going to let the AI control Melia, or even Shulk, and I don't like the idea of not having one (and only one) of them in my party) but I don't really want him to lose Aggro stuff as the less Melia gets aggro'd the better.
Mellia right now is the easiest one to get worked out with Arts but I know I'm going to have a horrible time deciding when I get more Summon Arts, currently she has Summon Wind, Summon Flaer, Summon Copy, Summon Bolt, Spear Break, Starlight Kick, Mind Blast, and Burst End. I have absolutely no idea how I'm going to make room for more Summon Arts as she learns them. I can, maybe, sacrifice Summon Wind since I don't really use the buff feature that much as from the Ether Up from Bolt (and Summon Copy by extension) so that her discharges are more powerful, and Burst End has been rather bleh so far.
I'm sure you can play through the entire game with any team, as the game isn't that hard (The only times I have died is taking on UMs when I shouldn't have in the early game (Tephra Cave early) and once way later into the game against a boss (the boss in the High Entia Tomb)), still doesn't mean it is good though. Shulk/Reyn/Sharla is rather weak from what I have experienced, Sharla messed up chains soooooo much and just slowed Shulk and Reyn down with her low DPS. I know a lot of people use this tea, for their first play-through because of how the game traps into thinking they are necessary but I didn't fall for the trap, well not for long anyway (I stayed with that party until I got to, like, the early phase of Makna Forest).The first time I've played the game my team was pretty much Shulk, Reyn and Sharla the whole time. Shulk offensive, Reyn tank and Sharla support. Only some of the battles forced me into changing the team. You just had one of them.