In my opinion, requirements #1 and #2 should be dropped, keeping only #3, #4, and #5.

Why? Well for starters, requirement #3 (Obtain all awards) requires that the Cruiser hull be purchased anyways as that is one of its achievements. Meaning if you satisfy requirement #3, you will automatically satisfy requirement #1 anyways.

As for requirement #2 (Obtain and use all skills), this requires a minimum of lvl 15 to achieve (assuming you only put 1 point into every skill). In my test 100% playthrough of Gunball, I only managed to reach lvl 14 and just barely missed lvl 15 (Off by 900 XP), and that includes me repeating a few levels for extra money. Requirement #2 also removes any possibility of different ways of approaching the run. In any%, I put most of my points into the money skill and some into damage skill, ignoring the rest for the fastest and (what I believe) most optimal way to beat the game.

By requiring that all skills be obtained, not only is the likely that you will have to repeat a few levels multiple times to reach that lvl 15 mark for all skills, but you also lose the ability to specialize in a specific skill.

TL;DR requirements #1 and #2 should be dropped, requirement #1 is already satisifed by requirement #3 and requirement #2 limits the potential routes for 100% and forces the player to repeat a few levels just to satisfy requirement #2.

I do agree that the cruiser hull requirement doesn't make sense, but I still think all skills makes sense to a degree.

One proposal I have is to change all skills to just obtaining all abilities you use with the spacebar, as the other upgrades are more or less stat changes rather than unlocking something new anyway, this way it still feels like 100%, but you can also specialize in money or whatever ability you choose

I could modify the rules of the category, but for now if they manage to meet the awards from the beginning, that's enough!