How well has the solenoid pusher been working for you? I've been reading up on those a bit, looking into a more compact bolt drive, but still have a bunch of questions. They seem smaller than the stepper, but have some problems of their own. lachlan_s's looks smaller than the Aliexpress solenoids, but it looks like it doesn't fail open. I haven't seen enough testing of either of them to know much about reliability or stable cycle rates, and both of them inherently impactful and shaky. At the end of the day, I really doubt there's a perfect solution, just different tradeoffs, as is the case with any engineering project. The stepper may be big and heavy, but damn it's smooth.
Definitely do a brushless build when you can. There's so much freedom in the design of the cage and flywheels, and the hy-con system in particular has amazing velocity consistency and is easy on darts. And the sound alone is worth the effort to make one.