I'll definitely add a lot of those things in a future update, I hadn't simply because of the fact that I didn't have quite as much time as I would've liked (I ended up discovering the jam two days before the deadline, haha) and I was aware of the upgrading a maxed-out upgrade, the reason for that is actually quite simple, because I was rushing and had a lot of "magic numbers" (numbers without variables attached to them for easy changing), the upgrade button thinks the max upgrade something can be is 4, when I reduced it to 3 due to time constraints. As well, there are two extra powerups that weren't able to make it to the end, that being LASER and ULTRA.
The big reason for the difficulty spike with the boss was also due to the fact that initially, the game was intended to have a "wave" system that would cause enemies to become more frequent and clump together more as you approached the timer, but my idea for it was too refined to implement in time (you were also meant to take 3-4 minutes to reach the boss, but I shortened it to 2 to make sure it didn't get boring with the lack of variety)
Also yeah a pause menu is more than feasible I just forgot 💀
(I also plan on making the roll give you i-frames, I hadn't done this as I feared it would be too powerful but given how the roll does not allow you to graze and throws off your aim, I think it's way too underpowered in its current state)