Start with 1 level of Fighter
As a melee spellcaster you need good AC and Con save for concentration, a single-class Warlock has neither.
That one level of Fighter will give you Two-Weapon Fighting and better armor until you reach acceptable Dex.
Str: 8
Dex: 15
Con: 14 (13+1)
Int: 10
Wis: 12
Cha: 16 (14+2)
The Charisma could be lower, as Hex is your bread and butter, but there is no better place for the points. At the first chance, get Resilient(Dex), for an even Dex score, and better saves.
Every level indicator is for character level, so subtract 1 for Warlock level.
Feats/ASI
Nothing raises DPR like an increase in your attack stat, it is about 15-20%.
L5: Resilient(Dex)
L9: +2 Dex
L13: +2 Dex
L17: Dual Wielder1
L20: Warcaster or Sentinel
Equipment
Pick up two Short Swords, and the largest Medium armor, as you do not have the Strength for Heavy.
Invocations
L3: Fiendish Vigor
L3: Agonizing Blast2
L6: Thirsting Blade
L8: Devil's Sight?3
L10: Armor of Shadows4
L13: Lifedrinker
Spells
By the level you take it
Cantrips:
L2: Eldritch Blast
L2: Green-Flame Blade (or Booming Blade, if you find very generous or stupid GMs)
L5: Frostbite, Sword Burst or Thunderclap, great when you would have Disadvantage on attacks
L11: Lightning Lure
Spells known:5
L2: Hex
L2: Hellish Rebuke
L3: Dissononant Whispers6
L4: Invisibility
L5: Hold Person
L6: Fear
L7: Fly
L8: Evard’s black tentacles7
L9: Banishment
L10: Telekinesis
L12: Counterspell
Further multiclassing
As a Warlock, you reach 90% of your full potential on level 12 in my opinion. You will never get any spell slots above 5th, and Mystic Arcanum is very far behind what full spellcasters get. You just got Lifedrinker and an ASI, time to change.
Rogue
Up to 9 levels. You will use Finesse weapons anyway, preferably next to one of your colleagues, so Sneak Attack is a simple DPR increase. Swashbuckler is good for Initiative, Assassin for critical, and Arcane Trickster gives new spells known.
Fighter
3 more levels. Battlemaster is great, but you can get some nice things out of Eldritch Knight as well.
Bard
Up to 9 levels. Lore Bards are awesome, both spells and Bardic Inspiration are great.
Sorcerer
Up to 9 levels. Metamagic is good, you can convert unused spell slots to Sorcery Points before short rests. Use them for Twinned Dissonant Whispers, or Quicened Hold Person for two critical attack from your Action.
Full Build
L1: Fighter for AC and Con save and Fighting Style
L2-L6: Warlock for Hex, Invocations, ASI and Extra Attack
L7: Bard for extra spells and cantrips and Inspiration
L8-L14: Warlock for Entropic Ward, Evard’s black tentacles, Banishment and Lifedrinker
L15+: Bard for more frequent Inspiration
1) Dual Wielder is popular and cool, but it is strictly worse than +2 Dex, as it provides about half the DPR increase. AC increase is the same, damage increase marginally better than an ASI, but +2 Dex also improves your attack. And your Initiative, and your save, and your Stealth.
Only take DW if you can not increase your attack stat, so once it is maxed out, or on 1st level as a Variant Human.
2) Agonizing Blast makes your backup ranged option viable.
3) You could take Devil's Sight earlier, it is popular with Darkness, but it is very party unfriendly, and I find it overrated. I would take it for a human, but you have Darkvision anyway.
4) Improves AC by one once you have 20 Dex.
5) As you do not increase your Charisma, I focus on spells that are not based on it, like Fly, Invisibilty, or Hex. Otherwise, I go for multi-target spells, so at least some of the them fails the save.
Take single target spells that you could upcast for more targets (Hold Person, Banishment) when you can already upcast them, or on the level right before.
6) Dissonant Whispers does not fit the criteria from 5), but is great anyway. Can target virtually everything, does some damage on a save too, and provokes Opportunity Attacks.
7) Arguably the best controlling spell in the game, and not even Sorcerers get it, so use it proudly!
Does damage, provides Advantage, imposes Disadvantage. Getting out takes an ability check, so no one is proficient, similarly, Magic Resistance only applies to the initial save. If an enemy manages to get out, you can push it back in.
Best Answer
Yes, an aasimar's angelic guide could easily be their celestial warlock patron, communicating with them through dreams
The warlock's description includes a brief exploration of the different ways in which a warlock might be in contact with their patron, including only via dreams (emphasis mine):
So the idea that the Warlock only converses with their patron via dreams is already given as a possibility by the Warlock's description.
And of the Aasimar's angelic guide, Volo's says that:
You could read this as meaning that the link the Aasimar has to its guide only functions in dreams, but it's also a valid reading of this text that they can only communicate through dreams, and that they still have a mystical link to their guide normally. Practically, it seems like the limitation placed here is more about making sure the Aasimar can't actively petition their guide for aid during waking moments nor receive direct, explicit advice or information from them (since being able to directly ask a Deva or similarly powerful celestial being for information or assistance would be a bit excessive for a first-level character).
Even if the nature of an Aasmar's normal connection to their guide is more limited, there is nothing which would prevent the Aasimar and their guide from making a more significant pact such as that between warlock and patron - that's what taking levels in the warlock class represents, after all. Perhaps the young Aasimar was guided by the dreams sent to them by their guide to discover a holy site or relic, through which the guide was able to make more significant contact; perhaps this Aasimar and their guide just had an unusually strong connection to begin with! As a DM, I'd quite happily work with my player to combine the background of the class and race in this way. Thematically they work very well together and there's no compelling reason to disallow it.
The guide could also be a higher patron's intermediary, if the guide themselves doesn't seem appropriate as a patron
Another plausible option is that warlock's patron is actually an even higher celestial being, but that the angelic guide is the intermediary who handles communication between the warlock and their patron. This might be a more acceptable option for many DMs, since devas, given as the typical example of an Aasimar's guide, are only CR 10 and not that powerful in the grand scheme of things - the text suggests that celestials such as Empyreans (CR 23) or Solars (CR 21), or even deities themselves, as appropriate celestial patrons. (The text does not rule out an Aasimar having an angelic guide who is one of these more powerful celestials, but that would presumably be very rare, and may not be doable if you've already established that the guide is a lesser celestial of some kind.)