Take Mobile, Alert, Sentinel, Tough, maybe medium armor master. Warcaster after coming back to Fighter.
At level 6 and 7, take Warlock levels. Hexblade patron.
Cantrips: Eldritch Blast, Toll the Dead
1st level: Hex, Hellish Rebuke, Healing Elixir
Invocations: Devil's Sight, Agonizing Blast
Should look like: F1-F2-F3-F4-F5-W1-W2-F6