Another player (not in speedrunning communities) showed me that it's possible to quickly go to the next level right after defeating a boss by quickly pressing F2 twice. I tried it out here, albeit I got a bit nervous and mashed the key ^^' Could this become a strat?

The same person said that missiles are limited by number and not by time, so they are used only when the player shoots.

Woah, that's really cool! I think that might actually be a new strat, possibly save a little more time.