I'm in the middle of my first manual pitch correction and am wondering
(1) if I click apply, it renders the audio and the keyframes are gone?
(2) after I click apply, if I want to make an adjustment (let's say I overcorrected a note), I would have to apply a new pitch correction effect on the rendered audio?
(3) is there a way to save the keyframes and make fine adjustments to them and then apply it to the original audio, so that the final audio is subjected to only one pitch correction, instead of multiple corrections?
You are probably over thinking it. Manual pitch correction can do wonderous things (within reason) and handles 'fine adjustments' very well. Obviously you want to avoid going back and forth making massive corrections of many tones or semitones but it is not uncommon to go back and forth making fine adjustments without issue.