First 5e character: help me building a gish warlock

[Selion]

Ok, i made up my mind, i'm well aware that the most effective way to increase weapon damage is going 1 level fighter, but i'll forfeit the DIP to rush to level 3 (PBF are usually slow, so i don't want to sit a year waiting for my build to come on line), furthermore i figure my character as a nimble fighter blessed by obscure powers, so the polearm master tank doesn't fit too much with the concept.

Then... Human, high stats in dex/cha/con (in this order) bonus feat in medium armor proficiency. I'll use eldritch blast until level 3

level 2:
Invocations: agonizing blast, devil's sight
level 3: pact of the blade (rapier)
level 4: either resilient (dex) or war caster (shield master could be a viable option too)
level 5: thirsting blade
level 7: invocation... well, i don't know, either misty vision or eldritch sight, or another free 1st level spell invocation
level 8: stats increase (either dex or cha, probably dex)
level 9: invocation- levitate at will
level 12: lifedrinker

I'll use armor of agathys and hex as main combat strategy, darkness in hard fights and occasionally thematic crowd control spells, like phantasmal force or black tentacles
Out of combat i'll focus in utility spells.
The only thing i don't like with this build is that i'm using a blade and a 1st level concentration spell just to keep with the eldritch blast damage at level 11.
It's not a powerful build, i just hope i won't fall too much behind my comrades, but i'll likely still be the closest thing to a full caster we have in the group, so things hopefully shouldn't go too sour.