You don't actually have to wait for anything. You can get to the boss in 1 minute. You get to hover both from gun recoil and from shooting enemies, which is how you keep staying midair and preserve momentum.
You can jump-evade and momentum-evade boss attacks, as well as parry projectiles and the head, so in the end it's only risky to get stuck below him and when you are overly aggressive with the kicks.
Machine gun turrets still die to one hit from anything else than the gun, so you can take them out immediately with one good kick, sneak up or break through with momentum when that fails.
Holding trigger is for... immersion. The thought of making it automatic passed through my head, but it didn't sit right with me.
I'm not sure what do you mean by automatic wall jumps?
Thanks for playing.