i didnt do my car "my" right way. but its up to you and what you feel should be improved with priority.
if i redid mine over again, i would do interior first, then suspension/braking/wheels, then exterior, then engine. you spend your time in the interior, so making yourself comfortable is the first option, plus this allows you to learn to drive the car stock, and to see its capabilities on stock parts, while making yourself feel the best inside it as you can. then you work on the suspension/braking/wheels to get it to drive and feel good, then whether you do outside or engine after that is a toss-up. depends if you want to look cool or go fast more.