Glacius is mostly a control weapon get Gf,Polaris,Final Flourish and the Shivermist Buster for a little bit support.Now for Def gear you should get some shadow and Elemental gear as T3 missions require all types of gear so you might wanna gear up!

Kasdriu, I have a detailed sword guide written for people in your situation. It gives a direct comparison between Acheron and Gran Faust, and it discusses your options in armor.

To respond directly to your points: If you like GF better than Acheron, then go with it. If you want to try other shadow weapons: Umbra Driver and Sentenza are your main options in guns. The other one is Biohazard, which is fun but weird. Dark Retribution is your main option in bombs. The others are Graviton Vortex, which is fun but weird, and shard bombs, which are not great.

...you have trouble killing jellies?!

There, now someone said it. :B

Personally, I would stick with your Nightblade and Frostburst lines for now, but that would be merely out of cost purposes. The Faust recipes are only obtainable through Basil (or other players who've purchased them from Basil), which can make them prohibitively expensive for a first weapon.

You may want a flourish in there, just so you can switch your weapons out according to the situations - whilst wolvers and chromas aren't enough of a problem to warrant an extra weapon, trust me when I say that devilites and greavers are. The extra damage type will allow you to accomodate for all situations, so that you can deal more damage.

You'll probably also want a handgun in order to deal with turrets. Polaris and Supernova are good for turret-suppression, but poor at cooperative play, and are troublesome if used wantonly. The Antigua lines are easy to use, fast-firing and mobile, but have low damage per bullet, meaning you'll need to keep up a constant rate of fire in order to kill monsters with it. Drivers take more skill to use effectively, but are devastating in the right hands, and easily capable of OHKOing a turret in a single charge shot, if you're in a small party. I wouldn't recommend most other guns for your current purposes.