If I recall correctly, every monster in there is a gremlin or slime. So shadow weapons are all that you need: Acheron/GF, Umbra/Sentenza/Biohazard, maybe Dark Retribution. For completeness I should mention Graviton Vortex, although I haven't tried a vortex bomb in there. GF might outperform Acheron, because it lets you keep slimes at bay by knocking them back.

Edit: And a crowd-control bomb might be nice...Shivermist Buster, I'm looking in your direction.

For armor you want normal (presumably), piercing, elemental, fire, and poison. Unless I'm forgetting something, only SFSC has this many armor requirements. For sworders, Vog Cub is an obvious choice, maybe with a little Skolver or poison UVs. Of course Dragon Scale is perfect, and Volcanic Salamander and Deadly Virulisk seem good, but very few people have those lying around.

I used the vog cub + deadly virulisk hybrid. In the end I found I was still dying quite a bit due to fire. So I decided to forgo the virulisk for full vog (any other fire resist sets will work too, of course) and I found it much easier.

Volcanic Salamander Mask/Suit + Poison max uv + fire low uv
Deadly Virulisk Mask/Suit + Fire max uv + Poison low uv

This will give you vh slime damage, and should give you immunity over fire & poison. If the two low's as 2uv's aren't enough, then maybe a med each. Unfortunately, we wouldn't know without testing.

But I'm happy with my dragons scale set + minimal uv's as already mentioned. The damage would be nice, but not at such a high cost.

Shield: Dragon scale shield. This is obvious, it resists everything the level has to throw at you. A BTS is doable once you learn the ropes, but if you're ever stuck in a hairy situation, it'd break too quickly.

----At this point onwards it's now just "recommended" not the "best"

Weapons: I can only comment on swords and guns, also I really would only do the run when solo or in pairs, just because the scaling of hp on the monsters make the run more annoying, at least for now until i can get better, so keep that in mind if you were planning to do full 4-man teams.

Swords:
Acheron vs Gran faust
- I prefer the gran faust because of it's larger swing. With Med damage, a gf combo will take polyps, slimes and most gremlins out in one combo, when solo.
- Acheron has great single target damage, whether combo'd or shield canceling 1st swings, but it's usability is reduced to do a) movement from the full combo, putting you into hazards and b) your shield catching on oil spills, minimizing your ability to shield cancel quickly.

Guns:
Umbra - Shoot and forget. The fact that there are lots of mobs and walls mean the bounces are doing decent damage. In the last room on the last wave, I only focused on shielding when the big Toxilargo attacked, and making sure that bottom switch remained activiated. just make sure you're not stalling by shooting too quickly and forcing a reload.
Sentenza - Great for switches and breaking blocks. There's that one room where you need to drill to the switch fast to get the water and make the place safer. Fast weapon for taking out a mob you know has very little hp left.
Biohazard - This required too much thinking. Slow bullets with tiny hit boxes mean you need to aim. Yes it's nice being able to get off 2 shots and not reload vs the umbra, but the advantages stop there. Also, you probably won't have time to use the charge, so half the benefit's gone.
Polaris - once in a while the 1st level will spawn some gun puppies, so this gun would be useful. The shock and knockback is useful to get some breathing room, even against gremlins. Just don't be that guy who can't put it away.

Bombs:
Shivermist - useful, but I only used it once in my last solo. I think in larger teams, it'll be more important (especially because not everyone has immunity)

Currently I use this:
Gran Faust
Umbra
Sentenza
Shivermist
I'm thinking of using a polaris in place of one the sentenza or shivermist, but I haven't decided. If you haven't already noticed, I've leaned towards weapons that do multi-target damage. This makes sense since things usually spawn in groups, in this sense a vortex or the new shadow shard bomb will do wonders, but the dark retribution is also useful.