There's no next step. There's no steps at all. There's no ladder to climb. You need the device which is suitable for your next project. That's it.
It's the same as everywhere else. If you have a job that requires nails, you use nails. If you need screws, you use screws. And you need a little bit of experience and little bit of brains to tell these situations apart.
Other people will recommend what they have used (and liked) in the past, whether this is suitable for your project or not. These people have completely different skill sets and levels, which are very different from yours. What is good for them may be different from what is good for you.
When doing microcontroller projects, 80% of skills is the ability to select a device which will help you to do the job the best. Note that this depends on many factors including your skills and habits. The device which I would select may be totally inappropriate for you. It takes time to figure this out. You need to try things, make mistakes, and the more mistakes you make the more you learn.
So, go ahead. Make your first mistake. That will be a good start.