I don't think the tunnel vision issue is something to fix. It was just something I noticed was happening with me, but wasn't caused by the colour of the bullets or anything. I was just thinking so much about lining up jumps that I was ignoring the bullets. That's also partially because I knew when I was jumping, I was over top of them and when I landed, bullets were destroyed so in either case, they weren't really affecting me so I could ignore them. So it's not something to fix, just a weird emergent property of the game I thought was neat. It's just something you need to think about a bit more as the game gets harder. And I think most ways to try 'fix' this issue that I don't really think is much of an issue would make the game less fun.
For the movement, when you move right, your movement vector will be Vector2(1, 0). When you move up, it will be (0, 1). The length or vector2.magnitude() will be 1. But of you're moving up and right at the same time, it will be (1, 1). The length of this is 1.4. Use Pythagorean theorem or vector2.magnitude() to check. Then this number gets multiplied by move speed and that's why you move faster. What vector2.normalize() does is cap your vector's magnitude at 1. So after you normalize, it will look like (0.747, 0.747) which has a length of 1. And your right vector (0, 1) will be unchanged because it already has a length of 1.