My gunner equipments are fairly easy to obtain.

Full shadowsun
Swiftstribe buckler
Damage trinket
Ctr trinket

This amounts to max'd damage, ch ctr, and high asi. A decent set of stats for people with no access to a seerus mask. Generally, damage boosts are great because they up your total damage output on everything. Gun bonuses tend to vary, it all depends on the weapons you use. Alchemers and blitz's benefit from ctr, while callahan and antigua line benefit more from asi than ctr.

Polaris is not a gun, it is a utility weapon. Don't call it a gun for dps'ing purposes.

Depends on if you want piercing, shadow, or elemental defence. Assuming piercing/elemental, you'll have asi already on your gun. Thus, you need damage trinkets to actually do something real with those shots. If you go shadow, you'll have damage, and either want asi on uvs so you can use heart trinkets, or asi trinkets.

Damage helps your low hitting shots to put the hurt on opponents. Asi helps you get into the dash faster after a shot, and I believe shortens reload animation should you ever be reloading during a fight.

Seerus mask is a gunslinger oriented helmet/head/top/mask. Ctr med and asi low, a total of +3 bonuses to a gun when most other sets only have +2. With a seerus mask, the shadowsun body, and a swiftstrike buckler, you get ctr vh, asi vh, and damage med. 2 damage trinkets boost your damage to max, or you can use the trinkets to max out asi and ctr. Its a total of more bonuses to a gun. About 1 asi's worth plus 2 ctr instead of 2 damage/asi.

Polaris mechanic destroys its own dps. Knockback on expanded shots, more damage on said shots. Unless you shock very very often, you push the enemy away with each shot. This also pushes enemies away/into teammates. Say a teammate was charged and is coming in from an angle to catch as many enemies as possible. You decided to shoot into the crowd because polaris dps is a;wihegjke amahzing. Congrats. You did less damage with that 1 shot than what your teammate could have done with his/her charge of brandish/da/alchemer/rss/basically anything but some exceptions.

The knockback is a great tool to keep enemies away, or herd them into/out of something. Most of the time though, sword knockbacks are enough. If not, just about everyone uses a shield anyways. Sure, you can herd enemies into a corner to cancel the kb. But by the time you do that, your team has to wait for you to finish, otherwise their hits might miss and waste their effort.

Unless you're in a team of all polaris.

Or solo. In which case, nobody cares what you do as long as you don't beg over and over for someone to heal you.

Asi does not make ur bullets go faster. If it does, it is unnoticeable. Asi shortens times between shots and perhaps reload animation. Not all the way sure about reload animation, but most likely.