I actually did discover chain dash! That's an interesting one. I can't say I like the fact that last jump lacks inertia and animation-locks you, but chaining jumps and dashes is kinda cool!
About cooldowns - you may consider introducing them, specifically for balance purposes, if that's your biggest concern. As for slots - switching might complicate things, but increasing the number of those could be an option. Or, you can allow to pick up abilities only into the slots. This way, you won't be able to hoard anything, and will be forced to pick up and use whatever gets available to you, and keep it in in your arsenal until a better option is available or until it's all used. You might also give enemies specific drops when they are hit by an ability of certain color, to encourage the use of abilities over the main weapon, making it preferable to always attack with spells. Wold be kinda hard to explain it, though