DVS is good for JK fights. Keep it.
Acheron vs gran faust has been debated many times. Genrally accepted is, acheron has a better charge, more dps on single/low number of enemies. Gran faust has... everything a heavy sword has. Think of it as a shadow troika.

BTB is a great sword, difference from flourish lines being the charge. Flourish has a charge thats basically a stronger combo. Btb charge is a spray of thorns outward, 5* having a snarby bite added along. Shorter range, more controls, less damage.

Consider adding a brandish line, as you might like it better than the avengers.

Upgrading to a gigawatt helps tremendously in a solo fsc run. Outside fsc, consider an alchemer in order to not annoy teammates with mini nitro blasts. Shock, nova, magma are all decent choices for alchemer lines.

Cat line is a preference choice, depending on your love of setting huge explosions up. Biohazard for the shadow damage in RJP

All good bombs at 5*. What about electron vortex? Similar to grav, but elemental, and chance to inflict shock. Takes krogmo coins to obtain recipes though.

I have no experience or knowledge with angelic sets.

Split elemental/piercing defence is not widely popular, due to normal damage in all tiers and strats. It is good in a general purpose set, but becomes useless when you understand what damage you take most in different strats and start building specialized/normal defence armour.

Wolver line is popular for swordmen. Vog for asi/elemental+fire, and skolver for damage/piercing+freeze. Vog is great for fsc and vanaduke runs, but any experienced player can take minimal fire damage in there. Either way, you can complement the missing asi/damage with trinkets. The vog basically replaces the divine set for swordsmen. Or used in the popular divine veil+skolver set. General purpose, defends from almost everything.

Owlite is a great elemental shield, and the fire resist makes it popular in fsc. Yes, volcanic plate is better for most of vana fight, but owlite is effective outside of fsc in almost any strat. Elemental is present almost every clockworks depth.

Scary skelly is a decent shadow set, the shield being the easily accesible shadow shield in the game. Crest of almire, from blackened shield of vaa boss reward, is considered best shadow shield. Takes time to get though.

Snarby shield is a great shield to get. Swordsmen's shield, with damage bonus med at 5*. Good amount of piercing defence. Ironmight and one of the jelly shields are supposed to be higher in piercing, but not a noticeable amount. Those are good for non sword users.

Nope. I don't touch the cutter line. But I've seen it used well. And that headbutt/touch damage is just... really off. Hard to dodge, even at max sword range with a faust.

The people I've seen it use well tend to be the ones with full 5*, and speed running RJP while carrying new players. They use the dvs until poison, then switch to something else.

edit: The damage by being close seems to happen less if you are not the target it's following. Still gotta smack it from as far away as possible though.

It's a bit tricky using a DVS on RJ. You cant use the full combo, just do like 2 swings and then back off or shield and get bounced out.

Your sword and gun plan is sound. All three of those alchemers are good. I'll let more informed people sort them out. Ash of Agni is great, really. But it has been argued that Voltaic Tempest does more damage against dense crowds, because shock has an area effect (that is, it damages non-shocked monsters nearby). And Voltaic Tempest is helpful in FSC, although it's not even remotely necessary, whereas Ash of Agni is not helpful at all.

People like Volcanic Plate Shield for Vanaduke and trojans in FSC. But really Grey Owlite is perfectly adequate, so I would not get VPS any time soon. I gave fairly detailed advice on sword armor above. For bomber armor, definitely read the Bombing Guide (and get Volcanic and/or Mad, probably). For gunner armor, you can figure it out as well as I can (and get Justifier and/or Nameless, probably).

My general advice to you is to work on being a good sworder (or gunner, or bomber) first. Get one set of equipment good enough, and learn it well enough, to be able to farm FSC, try a Shadow Lair, etc. Once you've done that, you can branch out into the other weapon styles, if you're still interested in doing so. Work deeply, then broadly.

You can basicaly get good at selecting gear by reading random wiki monster/armor/weapon pages. Be sure not to see everyting as an individual part, factor in weapons, armor, and monsters to your loadouts. Plenty of good suggestion threads out there.
On a side note, if you want the valkyrie helm, make dragon scale mail. You will be pleased when using this with a grand flourish on beasts or feinds.

"People like Volcanic Plate Shield for Vanaduke and trojans in FSC. But really Grey Owlite is perfectly adequate, so I would not get VPS any time soon. "
VPS takes celing tile hits and club swings muuch better on vannaduke. Leave the elemental defense to the armor, that's the part that actualy gets set on fire.

You could do Divine veil (veil has fiend bonus - mantle does not), grey feather cloak, skolver coat and vog cub cap. You'll probably want more later but this will give you a lot of mix and match potential. A general purpose set (Divine veil, skolver), an elemental set (Vog cap, grey feather), sword set (Vog cub, Skolver).

In this set up I would do at least Armor of the Fallen from your angelic set so you can pair it with the Vog cub hat and have shadow/elemental and full fire resist for vana runs. And maybe do the Valkyrie Helm to have a neutral shadow set (neutralize the negative fire and fiend damage).

To finish off to have both a full piercing set and nice Shadow Snarby set might I suggest a Deadly Virulisk Mask. You can pair this with skolver coat and BTS to give you max sword bonus in jelly king runs (and med jelly bonus with gun/bomb). Then pair it with Armor of the Fallen to get you shadow/piercing and full poison for Shadow Snarby.

So in review this will leave you with general purpose, full piercing (max damage jellies), full elemental, full shadow (no neg), a sword set, a good FSC set, and a good Shadow Snarby set.

(As an aside radiant silvermail is an option for shadow snarby too if you want something to do with that drake scale)

Shadow Lair Swarm Turrets deal massive normal damage. Evasion is best around those, but sometimes all you can do is block them to live. Normal defense should never be discarded, it shows up prominently everywhere, moreso than elemental as some of my friends say.