Best next upgrade?

Depends what you plan to do with the car. I'd build it different if I was planning to use it daily, versus if it was goi g to be a racecar or a cruiser.
It’s not a daily, have other cars. I live near a drag strip, but I’m not a racer. It may go there once or twice just for grins. Mostly a cruiser / fun car. Wrenching is half the purpose of it for me…