how much do the hashtags that appear on top of the title matter

This is one I'm actually not too sure of myself. I think the first hashtag is probably the most importance, from what I've seen. Including them anyway won't hurt anything though, so hey I guess it's nice to include them.

Is An Upload Schedule Neccessary? Having One Honestly Sounds Super Stressful

Not really. While yes it's important to remain consistent, there are YouTubers like Summoning Salt, MrBeast, and Dream that all post until their video is ready to publish. It isn't really important as many people make it out to be. Unless ofc, you wanna hold yourself to it.

Why did my latest video perform poorly? (I kinda already somewhat know why but would like insight)

idk, i don't know what your video was or what your analytics look like

What the most important thing for you at the time of making a video?

The most important thing would probably be the idea itself, as this is the time when I would come up with my title and have a general rough draft of what my thumbnail would look like if I did said video. Then using that, I would decide whether or not I would want to create it.