Luck caps at 80% yeah, totally forgot that, but I've ported that cap (phew)!
Crit chance does not cap: For every successful multicrit it is reduced by 20%.
For example if your tower has 100% crit chance for the first crit, the chance for the next multicrit will be 80%, for the next multicrit 64% and so on.
Oh okay, it is nice to know how the crit chance works.
I just realised that I forgot to ask about the item drop chance and item quality, does it cap at 100% or is it like the 80% chance for luck/something good to happen?