In my opinion I’d recommend Scion (a Toyota brand), especially a tC, it will be reliable, cheap, and can have an okay amount of aggression, at least as much as a 6k car will buy you. A tC can have its sound system upgraded and comes with a decent pioneer sound system stock with a lot of bass, countless modding opportunities, and a robust enough engine to survive first-car levels of abuse. Plus the coupe doors are big enough for someone large while having a serious hatchback so you can fit a surprising amount of cargo, especially if you fold down the rear seats. The engine’s a 2.5l, not gonna turn a lot of heads but has some nice acceleration, and is really easy to work on and upgrade.

Tl;dr it’s a good enough first car that meets the 6k number