Ultimate Optimizer's Multiclassing Guide

[Sir Stig]

Pact Magic and the Spellcasting feature don't stack. Three levels in Eldritch Knight will only net you 2 cantrips and 2 1st level spell slots that recharge on a Long Rest. So with that Level 20 build your spellslots will be 2(LR)/-/2(SR).

If you go with Arcane Trickster as suggested by Pete, then you will be able to hit that spell casting mark(level 5 combined spellcaster).

Aha! I missed a beat.

He is high on Dex and Cha, medium INT, so the arcane trickster is meh...
Back to the think tank. I think I might as well start a new thread when I refine the concept, since my brilliant idea had holes in it :) Thank you (and Pete) for your input.