When would it be most effective to multiclass into warlock as a 3rd level swashbuckler rogue?

Question

I am currently playing a level three Satyr Swashbuckler Rogue with the Sailor (Pirate) Background. I want to multiclass into Warlock, but I still want to be at least okay in combat with my mostly min-maxxed party. My current thought is that it seems reasonable to multiclass at level 5 or 6, and I'm considering both the Fiend or the Genie. We are planning to go to level 14. My stats are 8 16 14 10 10 16, and I primarily use a rapier.

I know that a Rogue/Warlock multiclass is not very good but I really like the flavor and want to make it work. I've been looking at maybe booming blade and eldritch blast for the cantrips and going to second level for invocations like Mask of Many Faces to help with non-combat encounters.

I have all sources available with the exception of unearthed arcana and Plane Shift.

I want to stay with rogue primarily, but I'm open to alternatives.

My party is a High Elf Illusion Wizard, a Variant Human Bear Totem Barbarian with the Sentinel feat, a Base Dragonborn Conquest Paladin, and a Lotusden Halfling Beastmaster Ranger (from Tasha's).

If I need to include any other information please let me know, this is my first time asking a question. Thank you!

Answer 1

Roleplaying: If you want to multiclass, take it early.

Let me first address this from a play-experience perspective, rather than a mechanical perspective. You like the flavor of having some warlock, the warlock class is good for that. So go ahead and take it soon. There is a never a guarantee that a campaign will make it as far as it is intended to. Everyone says they plan to make it to higher levels, yet it often does not work out that way. Real life happens, DM gets burned out, etc. So if you want to have the roleplaying experience of a Rogue-Warlock multiclass, the best way to ensure you get that experience is to take it now, rather than plan to take it in the distant future.

Mechanics: Wait until 10th level.

The Swashbuckler Rogue is loaded with good features from levels 5 through 9:

5. Uncanny Dodge
6. Expertise
7. Evasion
8. ASI (taking +2 DEX here and at 4th will net you 20 DEX)
9. Panache

The trouble with multiclassing is that it puts off getting the good features from your main class. Panache in particular is a incredibly useful feature. If you took DEX +2 at 4th and 8th levels, your dexterity is 20, and at 10th level, the Rogue just gets an ASI that you probably don't need right now. So if you wait until 10th to take your Warlock levels, you won't feel like you're missing out on an immediately accessible feature that you really want.

Answer 2

What's your primary role in the party? What do you want to be able to do the best?

You mention wanting to be "ok" at combat, but unfortunately it's more the case that Warlock benefits from a Rogue dip rather than the other way around.

As a Hexblade/Pact of Blade Warlock, for example, you could shift to ultimately only using Charisma as your melee stat, but you're a Rogue, and it looks like you're the party rogue, so it's not like you can afford to dump Dex, Int, Wis, etc.. so you're going to be really multi-attribute dependent (MAD) to do the things your character class(es) are expected to do.

Given your background, and that you appear to be a melee rogue, you might want to consider The Fathomless instead of the two patrons you included.

Could you accomplish the same thing you wanted by taking the Eldritch Adept or one of the Shadow/Fey Touched feats? (Picking up Hex, etc..) without the multiclass dip?

Personally it sounds to me like you might benefit more from a Rogue/Bard combo than a Rogue/Warlock one - you're looking for non-combat utility, and the Colleges of Lore or Swords both bring something to the table that works well with your attributes, plus you have the added bonus of picking up some healing spells/abilities (your party doesn't seem to have a healer?)