I've been playing this game for months and still barely have a grasp of the class system, the lore, or even how to play the game, still needing to ask other people what I roll for attacks I made just a turn prior. I'm clearly the best person to give advice on this.
The only real spell you need is Eldritch Blast, my friend. It's a cantrip so you can use it a lot, it upgrades pretty well, and you get to shout "ELDRITCH BLAST" every time you use it which is just fantastic. As a Warlock I tell you that no less than 85% of all my attacks involve some use of Eldritch Blasting. I Eldritch Blast my enemies, I Eldritch Blast the dirt to make a dust cloud getaway, I Eldritch Blast the sky and get roasted pheasant. And then when my Eldritch Blast gets a push upgrade, hoo boy, I'm Eldritch Blasting people into other people and I'm Eldritch Blasting out the back of our cart like a rocket booster. Eldritch Blast this, Eldritch Blast that, there's no STOP to the Eldritch Blasting around here, why even go for anything OTHER than Eldritch Blasts.
Coincidentally our D&D group is nicknamed "Cantrip Abusers" but like, totally unrelated, I'm sure.