My picks:
-Chaos
-2 Pentas
-Fire resistance Sprite perk
-Crest of Almire (or SSB if you feel really confident/lucky/foolish)
2 Weapon:
-Voltedge
-Blitz
3 Weapon:
-Iron Slug
-WRH/DA
-Blitz
4 Weapon:
-Iron Slug
-Blitz
-AP or Griffin?
-WRH/DA/BTB(Solo/dmg) or Shivermist (Team+support)
Explanation
-Armor/Shield/Perk/Trinks: FSC is full of large groups that are best dealt with with AoE attacks. Most AoE attacks are charge attacks. Chaos is great for buffing those. The Fire perk helps mitigate the fire vulnerability, but it's still there and carrying remedies is strongly recommended. For shields, none of these loadouts are sword-heavy, so BTS is a waste. Ancient Plate/Omega Shell are better for the Vana fight (APS blocks one vana hit right?) but really, you shouldn't be getting hit by him anyway and if you do, you'll be severely crippled regardless of your shield. SSB is nice because ASI, but it's not actually a shield in T3, just an ASI high trinket you wear on your wrist. Take only if you have supreme confidence in not getting hit ever. CoA is the best at resisting all the main sources of damage in FSC: Zombies, Trojans, and Fire. Offensive shields aren't really required anyway since Chaos makes up for them.
-2-Wep: with 2 weapons, you need weapons that do as many different things as possible (that you need them to) since you can only carry two. Voltedge has CC, knockback, interrupt, and solid damage. Not as much of any of those as some other weapons, but it does all of it well enough. Blitz is, of course, the Trojan-killer, and since the GU also provides some nice long-range poke with the normal attack. You could theoretically run Griffin instead of Blitz for mobility, but the damage reduction and the much harder time killing trojans isn't worth it imo. AP isn't really an option unless you're in a party because of how long it takes to kill Vana since it's no longer split Pierce/Ele damage.
-3-Wep: This essentially specializes more than the 2-wep setup. Replacing Voltedge with WRH and Slug because they do what Voltedge does, but better - Slug has better AoE damage and knockback, and WRH is better for single-target, close-range safe damage. Just be careful with the dash. Slug also has the added bonus of being a gun and having interrupt, so it can interrupt and kill leaping zombies and turrets. WRH also gives you some options for Trojan killing if you're in a situation that's too tight to use Blitz safely. DA is easier to use than WRH - no dashing into shadowfire - and has a more useful charge, but it's a bit lower on sustained DPS, I think.
-4-Wep: Even more specialized. Added BTB to the sword slot because with Slug, Blitz and an Antigua you have enough ranged damage for a sword to be only useful for keeping enemies off you that get too close. BTB is great for this because it's fast and has moderate knockback, giving you time to get into a better position to use the rest of your weapons. The Antigua - AP for the main dungeon or Griffin for Vana - allows you to be a more mobile, sustained-damage gunner and not rely on good positioning for Slug and Blitz charges. I could have put one of the Valiances here, but I chose Antigua because it's faster and higher-DPS, and Slug covers the knockdown/interrupt/knockback that the Valiances trade for that. Finally, if you're in a team and feel confident that they can keep enemies off you, you can carry a Shiver for the Vana fight and some general CC. It can also provide great setup for Slug/Blitz charges.
Post yours!
Gunner
5 star Sacred Firefly Shade set
Iron slug as your base DPS weapon
Blitz needle for Trojans and Vana
Divine Avenger for mass repositioning of monsters.
Electron vortex for Iron slug and party synergy.
Seraphynx
Disintegration ray for damage boost vs Vana and EV synergy
Iron heart attack for extra team support
Valkyrian Aura to allow for max Ctr DA charges when enemies get too close.
My prefered Vana shield would be Volcanic plate or Grey Owlite. Coa is nice if Slags trouble you.