Ultimate Optimizer's Multiclassing Guide

[Sir Stig]

Hi, I am new here. I am sorry if this is the wrong place to post character concept. If it is, you can give your thoughts about the multiclass combination, and disregard the fluff.

I just started playing D&D after 20 years pause, and as an old powerplayer, I started looking for ways to customize a premade Halfling Rogue (we were 5 players, not much time to create one from scratch).

Even though I emphasize roleplaying opportunities, I would like feedback if this build can also work strategically.

This is what I envision:

Cold Facts:
Main Class: Rogue - Scout, Mastermind or Swashbuckler (which of these would fit best?)
3 Warlock - GOO and Pact of the blade (GFB to boost damage)
3 Fighter - Eldritch Knight to get multiclass spell table lvl 4 (4xlvl 1 spells and 3xlvl 2 spells+ pact magic and invocations). Second Wind, Defense and Action Surge will all help the rogue survive and deal extra damage.
Bonus: I will have one Pact Weapon and 2 Bound Weapons available, perfect for a sneaky halfling infiltrator.
Option to take either fighter(extra attack) or warlock(thirsting blade) to 5th in order to get 2 attacks (Mastermind grants one extra attack at lvl 17 Rogue, but I may never get that far).

At Lvl 20 total I will have something like: Deceptive Rogue 12/Bladepact Warlock 5/Eldritch Knight 3 (4/3/3 spell slots + Pact Magic and invocations)

RPG aspect:
The rogue was attempted murdered (Glasstaff, no spoilers please), and I intend to play out the warlock gradually (puking leeches and such). I imagine he was in limbo/bardo and by some disturbance of the planes, he was tainted by the GOO. I hope to get a chance to use Arms of Hadar for revealing my warlock lvl. Thoughts about Warlock spells: (Infestation), Mind Spike, Hex, Devils sight.

If he gets too OP, he can go corrupt and get drawn into another dimension (taking an enemy with him ofc..)