I swapped out the cranks on mine, but not the BB. Honestly unless you're having actual problems with the stock one, I wouldn't bother swapping it out. Seems to be a normal well working square taper, so the door is open to 90%+ of the useful cranks out there. It's one area that "from the factory" you're usually ok... though any experts out there feel free to correct me, I'm still learning this stuff too.
My BB experience prior to this e-bike was a ashtabula to BB conversion I did on my regular 26" cruiser twelve years ago.
Thus why mine got converted to 130mm with a 53 tooth chainring with zero hassles. There's something about only having four connection points that irritates the crap out of my inner engineer.
I didn't look closely enough at the existing BB but with everything else in the drivetrain being Shimano, that's probably what it is.
If you do take the plunge could you please take some pictures of the process -- or even make a video? Help the next poor sod along? I really wish Aventon wasn't so painfully vague about the exact model parts used, but I guess like Apple that's how they can change vendors on the fly in the "race to the bottom" on parts quality.
Thus why even the cheapest parts off Amazon seem to be a better quality. I really should have done a DIY, but in hindsight the experience with this one means when it comes time to replace it, I'll be much better versed in choosing parts.