I don't have time to get to all of them right now, so we will start with the deadlift.
Your back rounding is actually far from your biggest problem. The back is the weak point of the conventional deadlift so it will round slightly whenever the weight gets heavy; how much you are willing to tolerate is up to you, and if your lower back starts to round just stop the lift because you likely won't be able to lock it out anyway.
Your back rounding did not look like a problem at all to me.
Your last two reps were actually better because the bar started more over your mid foot. The first two, I can definitely notice the bar drift back over your midfoot which is obviously inefficient. You need to start with the bar more over your midfoot, bend your knees until they touch the bar, then tip over at the hips as far as you need to reach the bar.
Next you need to figure out how to get your body tighter to initiate the lift. There are a lot of tips for this and I am not sure which one will work, but squeeze the bar as hard as you can and pull your lats into your front pockets to get your back tight. There are a lot more cues that might work, but I can't remember them all right now. Squeeze your abs as hard as you can whenever you take your big breath to start the lift.
Next, stop looking to the side. Keep your head and neck aligned, looking forward, because once you become more efficient and can lift more weight you can actually tweak your neck by doing this.
Finally, you need to focus on pushing your hips through once the bar gets above your knees. Fire your glutes as hard as you can at the top of the movement to fully lock it out.
