Cool! Yeah, I cleared the Extra Version recently as a reminder of some of the differences related to full-auto. Playing without rapid fire definitely requires a different approach to most sections, but you can actually get through most of the game without hammering the buttons at all. MathU does this in all of his videos, only tapping in a few key spots. The stages are still very manageable, for the most part, since you still cut through most enemies effectively, but it means you're more likely to see each boss's full range of attacks, and the ones some of them pull out when they're almost dead are terrifying.
The zone Q Captain was a total fluke in that run, to be honest - I haven't figured out how to capture it consistently yet but it moved the right way for me! I normally just focus on not getting trapped against the ceiling or floor by it. Zone D's is a bit easier to manage, though, since you can lead it wherever is most comfortable for you during its 'tracking' phases, get above it when it stops to bomb the orb, then pull back before it moves up toward you and starts tracking again. If you're on the right side of the screen, behind its head, the fireballs can't reach you.
Good luck with the no-death run - you can deffo do it! I'm guessing you only lost one life last time? I can't decide if I want to try a route that goes through significantly different stages, next, or just go 'all up' to Great Thing...