Aww Mel, you are doing so well!

So much of what you said reminds me feeding my DD through those early weeks. I think she would do pretty much all of those things you mentioned. But she got much, much better at feeding as she got older (as they do).

With the positioning not being right (bringing that bottom lip up) and changing during the feed, my DD did this and I used to hold her head with one hand and my boob with the other and kind of keep her clamped on so she couldn't move. I think I probably had a pillow under her body to raise her up. It seemed to work for me Actually I still hold my boob in position for her now otherwise she backs off and doesn't take enough nipple into her mouth.

particularly on the left side, she will do some fast sucks, and then not suck for a few seconds (maybe 20?) and then will suck really really hard.
She's probably just adjusting her sucking to your flow, so you're probably getting a let-down and she doesn't need to suck at that point, then the let-down will go and she thinks "hey, what happened, I want some more of that". Lots of babies, mine include, actually pull of completely during let-down and milk spurts out everywhere. Some people suggest you express until you get a let-down and then put them on so they're less likely to be fussy like that, but I never bothered, we just kind of worked through it.

More hugs and support to you!