Battleforged and Ace Stiker are exact replicas of each other so no worries.

With 295 ATK, Shout and AS would boost his ATK to 575, which is pretty close to soft-cap. He'll deal fairly respectable damage so don't worry about Basch's damage capacity. In fact, adding DD is less optimal than Pride of the Red Wings from a damage output perspective.

Balthier with 377 ATK pre-buffs, will hit 735 ATK post-buffs, which is more than sufficient to hit damage cap with spellblades, even for Seifer at weak state. Thus, there's really no point in equipping +DMG or +ATK RMs on Balthier when damage is capped. My best suggestion would be to equip dual cast Spellblades (Bartz RM2). This comes with a risk though as the second dual cast, if activated, targets randomly and hence might end up healing someone instead. If you're worried about that, then you could equip DEF/RES improving RMs or some other utility ones. You don't actually need to have RS armour to capitalise on the +30% DEF. It's just something to note as people sometimes forget there's a DEF boost on AS.

You don't have much of an option in terms of spellblades as you need Aerora, Blizzara and Thundara Strikes to hit all 3 medal requirements. One way to squeeze in Biora Strike is if you drop Lifesiphon from Cloud, and have both of them on spellblade duty, which may or may not be a bad idea since you don't have Battleforged on him. The other is to make Tyro your healer and drop Yuna for Agrias as your 3rd spellblader as suggested above.

How low are your DEF/RES? If you're equipping native 5* light armours (no RS needed), you should be fine. There's always a bit of RNG involved at the start to get sufficient mitigation up fast enough. Note that getting Protectga up first is more important than Shellga as their magic attacks are unlocked on only the second/third turn. Thus on the first turn Basch would be casting AS, Tyro would be using SG, and Yuna using Protectga, while Cloud or Balthier uses Shout.