>>714947642 (OP)
>combat
Auto-attacks -> Arts -> Specials -> Blade Combos -> Chain Attack
Driver combos exist both to stunlock the enemy and give you additional damage through either Smash or using Fusion Combo mechanics, I would recommend looking this one up because you can do some fun stuff with them and will especially speed up combat at any point in the game.
Seals produced by BC finishers can be helpful against certain bosses and challenge mode stages, but for most of your gameplay this mechanic can be entirely ignored.
Your party setup should be able to perform at very least one full blade combo path and it's ideal to have at least both Break and Topple.
>Blades and classes
Heavily depends on the blade's own affinity chart, but generally avoid shield hammers. Every other class has good rares, some better than others. Do not instantly discard commons, they can get very strong and unique combat skills along with helpful field skills.
The best class imo is Chroma Katana, coming with decent DPS, evasion arts, and generally dodgetanking is just better than the alternative.
As for story blades, once Rex gets Mythra you will feel the massive upgrade. Not that Pyra was bad, but she does not have something like foresight to double as both support and DPS.
Dromarch is complete trash, only useful for early Break and healing. Give Nia a Bitball and/or Ether Cannon instead. Or hell, give her a common twin rings with actually good skills.
Poppi doesn't get good until Poppi QTpi, from an optional endgame quest. But, once you get her and grind enough ether crystals, this is the single most broken blade in the entire game.
Brighid is extremely good as long you only use her and don't switch out. Her passive stacks up to some strong damage and if you know what you are doing you should almost never be in danger.
Pandoria is very meh until NG+ because of one affinity chart node on her driver. Basically don't expect much before you get that.