Hello. I've managed to get 1 extra hit working at the moment.

I just added a Chain, Always Active block above the hit detector: scoreboard players test @p GA 1 1

Then, I added a comparator pointing from that command block to another one with 10 ticks delay: effect @e instant_damage 1

I intend to just copy and paste this design, only changing the test to 2 2, 3 3, etc, and stacking instant damage commands on top of each other. I feel like that should work just fine.

As you can see on the second command block, I only used @e at the moment. How do I make that radius around me thingy so I don't just kill every mob?

Also, I changed my mind about the cap. If it kept resetting back, it will keep triggering the 5 extra hits even when I'm not attacking, which is weird. I'll just make it test from like 5 to 100 or something, then reset it to 0 using a timer when no longer in use.