Paladin build for Curse of Strahd

[Casualoblivion]

I'm building a Paladin for Curse of Strahd. Going variant human and oath of Vengence. I've taken Polearm Master as my feat, but that isn't final. I have a feeling I'm going to want to multiclass at some point, but I'm not entirely settled on when or how. Curse of Strahd goes over levels 1-10, so unless I do 1/9, 2/8, 4/6, or 5/5 I'm not going to get two ability score bumps. Paladin 6 has the good aura, and I think I want the extra attack.

I took Polearm Master as my feat because it seems the strongest at the early levels. The main thing that makes me think of replacing it is a spoiler I read that said Curse of Strahd features a Greatsword+2 at some point. I want to go offense, not tank. I'm playing at a table of newbies, and I'm not sure Great Weapon Master would be in good taste. Maybe take it as a capstone with my second ability bump, if at all.

Im thinking I'd rather go Sorcerer, for Booming/Greenflame Blades and Shield. Oath of Vengence and Sorcerer both get Haste as a third level spell, but it has been pointed out to me that I'm going to have trouble maintaining concentration on it so I'm not really going to miss it that much. I could also take 4 levels of Warlock instead, maybe.

The other question would be when to multiclass. With Booming/Greenflame, I can put off the second attack because those scale up at level 5. Grab smite, then take a few levels of caster, the go back and forth. Not sure the progression.

Decisions need to be made, any advice?

[Gtdead]

Even if you consistently proc their rider effects, scag cantrips won't outperform polearm master.

At lvl 4 it's

2d6+4(gwf)+1d8(bb proc)=17.2 vs
1d10+4(gwf)+1d4+4(gwf+PM)=17.3


At lvl 5

2d6+4+3d8=26.2
(1d10+4)*2+1d4+4=27.6

If you can make a lot of AoOs and somehow proc their rider effects then eventually scags will outperform polearm master. But without reach and reaction generation it's extremely hard to do. Since you will only reach lvl 10, I'd say just grab polearm master as vhuman and increase your str with ASI. Hunter's mark and GWM scale better with PM too. Using GWM on the bonus attack from PM is a nobrainer.

If you try to go for PM+Spellsniper+Warcaster, it may seem like a good idea, but the matter of fact is that you cancel the bonus attack by casting a cantrip, and you still need lvl 8 to use scags as a reaction so the damage will be worse due to having less Str. Your build will come together too late.

[Firechanter]

Disclaimer: I have no knowledge of the CoS module.

Concerning multiclass: so basically the only choice _not_ netting you 2 ASIs by the end is going 3/7....
OoV Level 7 is kinda an empty level anyway -- you gain a marginal feature that virtually never triggers (unless you have Sentinel maybe, in which case you won't need it either). You'd either go 6 or 8+ Pally levels.

You might also consider taking just 2 levels of Warlock. The main benefit being a decent Ranged attack (Eldritch Blast plus Invocation for +Cha to dmg) and 2 spell slots that refresh on a short rest. The latter really ain't bad, especially if you regularly get two Short Rests between long rests. Basically, you'd exchange two 3rd-lvl slots for six 1st-lvl slots so it's probably square.

Concerning the feat: you already pin-pointed the problem. Comparing strictly mundane setups, PAM is probably superior. But in actual play, magic weapons will enter play at some point. And here it's very clear that magic swords drop much more frequently than polearms of any sort.
If anything, you should check with your DM: are they willing to customize any drops to cater for your specific builds, or is everything going to drop As Written?
Personally I'd play it safe and go for the Greatsword, especially if you already know there will be a good one in the module. So of course that would point towards GWM for your feat pick. The question whether it would be "too much" for your table depends largely on what the other players are bringing.

If you don't want to go GWM for party balance reasons, another great feat for a Paladin is Resilient (Con).
If you think you're not going to be concentrating on combat spells anyway, you should also consider ditching Vuman and going Half-Elf instead. An awesome race for any Paladin - start with Str, Con and Cha at 16, plus Darkvision, what's not to like?

--

Personally, I am playing a very similar character right now. VHuman Vengeance Paladin with GWM as first feat, and recently picked up Resilient Con at 8, playing a DM-homebrewed campaign. It's not entirely optimized because I am stuck with Con 15 after the feat bump. Also, I haven't been able to get a lot of mileage out of GWM so far. At first, most enemies had too high AC to use Power Attack reliably. Then the opposition shifted towards monsters that had resistance vs nonmagical damage and I didn't have a magic Heavy weapon. At least I had a +1 Versatile weapon from a random drop. Had I gone PAM I would have been totally shafted. :6

All I'm saying is, you can plan all you want, but ultimately the DM has an awful lot of control over how much use you can get from it.

[Casualoblivion]

Paladin 7-10 don't seem like they do a lot for Vengence, aside from haste and getting the second ability bump sooner. The trade off for Sorcerer or Warlock means more smite. I'm not that concerned about the ranged attack, throwing Javelins isn't that bad. It's a tough call.

[Firechanter]

Word to the wise:

If your DM plays out your enemies with any amount of cunning, expect the Paladin to be a, if not _the_ priority target, _especially_ as GWF. You have the highest burst damage, you buff your allies with your aura, you are a spellcaster; and on the other hand you are very hittable (lacking a physical shield and the Shield spell) -- so you are a rewarding target all around.
Mixing in Sorc would gain you the Shield spell, but it's a very resource-heavy defense, and at the same time it reduces your HP total. So all in all I'd say it makes you an even more attractive target.

Again, my own experience with a OoV Pala is that my character is _by far_ the one who hits the canvas most often, and draws the most healing power from our Cleric. At the beginning of an encounter the enemies usually split their fire, but as soon as I start smiting they start focussing on me.

You might want to take that possibility into account when planning your character. Just saying "I don't want to tank" does not guarantee you won't be getting a lot of incoming fire.