I've played enough to have a strategy for every character including SoR and the bonus labyrinth. It's my favorite FF to just plow through even though 10 is easily my favorite.

With the core party, I go very similar to Marky. Firion usually has a sword and shield or 2 swords along with white magic. Maria is my black mage and either is an archer or given dual knives if the labyrinth isn't an option. Guy is given and axe and shield or dual axes and has all the buff spells, black or white. ALSO learn Toad, Mini, Death, Break, Teleport, or Warp and level it up. Even in the anniversary edition, you can 1-shot bosses with them (except the Dark Emperor or Zombie Borghen due to ploooooot).

The rest vary in how you should use them. Minwu is a White Mage, so USE HIM FOR THAT. Josef can be lacking in HP, but his attack and defense can make him somewhat of a tank powerhouse. Gordon is fast despite being squishy, so he can easily use items or help in escape. Leila is already dual wielding, but I change her sword to another knife and KILL EVERYTHING. Ricard, also short on HP, can become nasty in damage, especially in SoR, so give him the best lance you can and hope for the best.

With Leon and Scott....their HP and defenses are gross, but their damage output can be insane. Scott has the black magic on the team as well as a sword, and he can be a crutch for Minwu and Josef early on. Leon, meanwhile, can go a few ways. My favorite tactic is to give him the Blood Sword, a Fire spell, and a second sword or axe. The Blood Sword acts as a pseudo-heal for him, and he does more damage with it than Firion (since his Stamina is super high and will make his HP grow fast. I checked this.) Of course, then you have Longinus from the labyrinth, so that's always an option if you can.

Yeah....please don't judge me for the detail in this! I get bored!