Hexblade/Paladin Curse Bringer & Divine Smite clarification

[BabyCthulhu]

Can someone tell me if the following is correct?

Hexblade Warlock (Pact of the blade) 5+/ Paladin 3+

Action: Attack (Using Curse Bringer greatsword)
1st Attack damage 2d6 (greatsword) + STR mod + 2d8 (burning 1st lvl spell slot for Divine Smite) + 2d8 (Burning another 1st lvl spell slot for Curse Bringer's smite)
Extra attack= Exactly the same again.

So, is anything stopping you from burning 4 different spell slots in a round? Or stopping you from using both smites at the same time?

[RSP]

RAW I think you're fine doing this. Keep in mind though, UA material isn't written with multiclassing in mind, so probably not RAI.

[Mikal]

Can someone tell me if the following is correct?

Hexblade Warlock (Pact of the blade) 5+/ Paladin 3+

Action: Attack (Using Curse Bringer greatsword)
1st Attack damage 2d6 (greatsword) + STR mod + 2d8 (burning 1st lvl spell slot for Divine Smite) + 2d8 (Burning another 1st lvl spell slot for Curse Bringer's smite)
Extra attack= Exactly the same again.

So, is anything stopping you from burning 4 different spell slots in a round? Or stopping you from using both smites at the same time?

Looks correct to me, though odds are the damage will be higher if you use your Warlock spell slots, since by the time you get Cursebringer they will be doing 4d8 (CB) or 3d8 (DS) by default.
so, assuming you're wanting to blindly spend spell slots to burst as much as possible and not wait for crits, or choose one smite over another, and you aren't using the feat that gives you an additional 1st level spell...

If your Extra Attack comes from Paladin (So Warlock 3/Pal 5):
2d6+Str Slashing+3d8 radiant+4d8 Magical Slashing+Misc on up to 2 attacks (1 per long rest, 1 per short), in one round.

-and-

2d6+Str+2d8 radiant+2d8 Magical Slashing on up to 4 attacks (assuming 1st level Paladin slots), in two rounds (4 per long rest).

Using Paladin as your Extra Attack provider means you can sustain the nova for three rounds, after which you can only do so on a single attack every short rest.

If you're using Thirsting Blade for your Extra Attack (So Warlock 5/Pal 2) it becomes:
2d6+Str+4d8 radiant+6d8 Magical Slashing+Misc on one attack (1 per short, using both Warlock slots)

-and-

2d6+Str+2d8 radiant+2d8 Magical Slashing+Misc on one attack (1 per long, using both Paladin slots).

I know you said Paladin 3+, but as Paladin 3 only provides an odd number of spell slots the whole "double smite" option doesn't fit, since you obviously need even numbers to double smite.

Using Thirsting Blade for extra attack over Paladin in this case means you can only sustain this for a single round, after which it's double smite on single attacks between short rests for you. In addition, the total damage is slightly higher using the Paladin progression, so if you're trying to build a burster Paladin/Warlock multi-class, you'd be better off actually going Warlock 3/Paladin 5 if you're wanting it ASAP instead of Warlock 5/Paladin 3.

Higher levels skew the calculations as Warlock's eventually get 5th level spell slot damage that regenerates over a short rest vs. the more numerous Paladin slots, in addition to other benefits both classes provide.

All rolled damage doubled on a crit of course.
Plus if they survive movement rate moves to 0.

You'll burn through your spell slots like no one's business, but when you require a nova strike there's nothing quite like it.

Optimally speaking, you will want to use your higher level spell slots exclusively on Cursebringer whenever possible (due to the increased damage), and save your level 1 spell slots for Divine Smite, barring extraordinary circumstances such as magical slashing resistance/immunity and/or radiant damage weaknesses.

You'd also be saving such bursts for either crits that won't already kill the enemy, or for enemies you need to burn down ASAP regardless of resources.