Agree with culture on needing a BTB or Callahan for fiend/beast enemies. The Polaris already covers elemental damage very well - most undead and constructs are perfect targets for guns. DA would have reduced damage against beasts, and it's too slow to be useful against devilites imo. None of your other gun choices are effective against wolvers (their teleport dodges all of them - you really need callahan for dodging enemies, because they don't even try to dodge it. Or a sword/bomb.)

On your armor choices, I'd stay away from the divine veil because it has no normal defense (only one or two enemies per damage category actually do pure damage, even in tier 3. Normal defense is actually the most relevant because of this.) If you're set on getting a piece of the magic set to 5*, go for grey feather. As for your armor, deadshot is very specific - it only increases your damage against undead, and that damage bonus isn't actually gun-specific. It's not technically gunner armor, even though it branches from it. Nameless might increase gun attack speed, but that's not very noticeable on guns - it doesn't decrease reload time, and doesn't decrease the time it takes to shield after a shot, which are the two most important things to increase the speed on (sword attack speed bonuses decrease the lagtime after a full combo and allow faster shielding, which is why they're relevant)

It's actually hard to suggest gunner armor to anyone, even a gunner - the attack speed armor isn't useful for reasons stated above and has no status defenses, the damage bonus armor only grants a single level of damage bonus and has poor defenses (piercing defense, penalty to poison resistance) and the deadshot armor is actually not gunner armor and has a mostly irrelevant resistance on it. You'd actually be best off with a piece of vog/skolver to buff your one sword.

On your trinkets, the elite modules are fine. The jelly bands are unnecessary - not only do they do very little to actually help you, most piercing attacks in the game are melee. As a gunner, you shouldn't be in range for them to hit you, especially if you're carrying a callahan. The ones that are ranged should be coming from a large enough distance that you'll have time to dodge or shield anyways.