Sharpness - the damage formula is +1 damage for level 1, then + 0.5 damage for each level beyond that. As far as I know in vanilla Minecraft, the decimal is rounded down and never used. So the damage table looks like this:
I - +1 damage
II - +1 damage
III - +2 damage
IV - +2 damage
V - +3 damage
VI - +3 damage

Suggestion - remove Sharpness VI, or make even levels of Sharpness do something.

Featherfalling - Featherfalling IV provides a protection level of 12. Using an Ancient Tome to reach V lets you reach the cap of 20 with Protection IV on the same pair of boots. (Since FF is the only enchantment that don't conflict with Protection, and since you are pouring SEVENTY LEVELS into your boots, I think that assumption is safe.) But that is also assuming 3 other empty armor slots. I think FF IV puts most players at the cap, already, and level V is useless.

Suggestion - remove Featherfalling V, or let it break the cap at level V. Why can't I be immune to fall damage?

One more, but I'm getting nitpicky: Bane of Arthropods VI. The two insects in the game with the most HP are the common Spider (16) and the Cave Spider (12). Neither have armor. At level V, which is normally obtainable, the damage bonus is +12.5. Using an ancient tome to get +15 damage is never helpful or noticeable?

I'm pretty sure the decimal is used. Health is represented internal as a floating point number, then is rounded up to the nearest 1/20 to be rendered. A +0.5 damage boost does stack up very slowly over the long term