Could Use Some Advice for My Warlock's Future Career

Would like some ideas and suggestions for the future career of my warlock. Here is what he currently is at level 3. The GM will allow us to do some retcon of the build.

Tiefling, Warlock 3, Pack of the Tome, The Great Old One, Agonizing Blast, Book of Ancient Secrets, Repelling Blast
Str 8, Dex 14, Con 14, Int 12, Wis 9, Cha 17
Spells: Eldritch Blast, Minor Illusion, Guidance, Mending, Resistance, Thaumaturgy, Dissonant Whispers, Tasha’s Hideous Laughter, Hex, Hellish Rebuke, Armor of Agathys, Shatter

I had originally envisioned him as primary a debuff caster, secondary a blaster, and tertiary a backup face character for social interactions. In actual play as his personally more fully develops, that has altered somewhat. While the debuff caster and blaster aspect have been about as reasonably successful as could be expected at our level, those have become secondary. He has been the primary face character (with a strong focus on pathological liar and con artist). He has more often and more effectively been talking his way around encounters and/or creating a distraction.
As such, I’m finding myself wanting to have a few more skill and tool proficiencies than are usual.
I would like to be expert in the use of disguise kit, deception, persuasion, sleight of hand, and stealth at a minimum. However intimidate, thieves’ tools, insight, perception, and investigation would also be extremely useful for the situations I’m putting myself into.

I’ve been looking into some of the possibilities. Obviously I can’t do all of them. I only have the Player’s Handbook and GM’s Guide so far. Was planning on another book or two fairly soon. Definitely the Monster Manual and maybe Xanthar’s Guide to Everything.

(I’m fairly new to 5thEd so correct me if I’m wrong on any of this.)
Multiclassing with a level of bard - 4 bard spells known, 2 slots of 1^st level each day, a skill proficiency, plus bardic inspiration.
Multiclassing with a level of rogue - thieves’ tools, a skill proficiency, expertise with 2 skills, d6 sneak attack (does this work with Eldritch Blast), Thieves’ Cant
Feat Actor – Cha +1, advantage on deception and performance when trying to pass myself as another person, and mimic speech
Feat Lucky – 3 luck points for a reroll each day
Feat Observant – Wis +1, read lips, +5 to passive perception, +5 to passive investigation
Feat Skilled – prof with 3 skills and/or tools
Amulet of Proof Against Detection and Location -
Ring of Mind Shielding -
Gloves of Thievery -
Spell Disguise Self – duration is pretty short though
Cantrip Friendship – not bad except duration is short and then they are pissed
Spell Charm Person – good one

Are there other feats, spells, or magic items that give proficiency and/or bonuses to these type of activities?
Suggestions on which I should prioritize or ignore?
Do some work better, worse, or at least different than might be expected?

Usually a 3rd level warlock only has two invocations, not three.

Usually a 3rd level warlock only knows four spells, not six. Since you already get Hellish Rebuke as a race ability, you might decide you don't also need it as a spell.

Ring of Mind Shielding is nice, but you get that ability at 10th level automatically so by the time you find one you might not need it. In any case, a tomelock shouldn't worry too much about gear. A full ritual book costs as much as a dozen minor magic items -- it'll be a long time before you can afford anything else.

Personally, I feel the same way about Charm Person as you do about Friendship cantrip: short duration and then they are pissed.

For Disguise Self, I assume you mean the invocation, so you can just recast it every hour. I really like it, it's amazing, but if you use it all the time the other players might not know how to deal with it. Even if they are ok with it, the simple fact that you describe your character's armor, gear and looks four times every session while the other characters describe their armor, gear, and looks once every four sessions can either become tedious, or seem like spotlight hogging. It can become a real impediment to their ability to roleplay with you. I like to make sure I include a little sign so they can always recognize me (I use a pseudodragon -- every illusion either has one tattooed on an arm or decorating a shirt or dangling on a necklace or painted on a shield or whatever). But... go ahead and try it; worst case, you just switch it out for a different invocation the next level.

Feat Skilled is not real popular but if it's something that suits this character, go ahead and be unoptimized. You'll be happier for it.

However, in practice, I think the sooner you get your charisma to 18 the happier you'll be. That limits your options considerably. Think of it this way: At level 4, the Skilled feat gives you +2 to three skills, a total of six plusses (but that soon jumps to +3 with three skills). But just bumping your Cha and Wis instead gives you +1 to nine skills, a total of nine plusses -- PLUS the improved saving throws, attack rolls, more agonizing blasts, etc.

Actor seems iffy at first, but remember it's stronger for a GOO warlock than anyone else for two reasons: First, it can improve the effectiveness of your Disguise Self illusions. And second, if your DM allows, it can improve the effectiveness of your telepathy so you sound like other voices in their head. Since you have Minor Illusion, your DM will likely also allow it to enhance the voices in your illusionary sounds. Normally I wouldn't care too much about Actor, but let's face it, your character is perfectly built to get the maximum out of that particular feat.

Yeah, I made a couple mistakes in that first post. It was supposed to say Book of Shadows was the next invocation I take. Unless I trade out repelling blast for it. And yes Hellish Rebuke is a race spell not a class spell. The other is from The Great Old One.