Hello, combat team programmer here!
I’m gonna try and answer #3 as well as possible without going into absolutely every detail and making it too much of a wall of text.
First off, there is actually two cleave values behind the scenes, one for attack (dev term for Damage) and impact (dev term for Impact).
But this is mostly for legacy reasons from early implementations, and in actuality the highest of these values are used for the hit mass budget calculation. (And both, and therefore the final, value should be influenced by buffs and other bonuses.)
The absolutely shortest answer to #3 is that the calculation for the which enemies can be staggered are done the same way as for damage. But we should always apply some kind of stagger or hit reaction as long as the weapon haven’t been stopped in its sweep.
The more technical answer is along these lines:
All hit mass decide is “will this target stop the attack, or let me cleave through to the next one in line?”. Then the damage profile for the weapon can define (somewhat simplified) that “target 1-4 will take diminishing health damage and target 5+ no health damage, and target 1-6 will receive diminishing staggers, and target 7-infinity will take a step back”.
Almost all weapons will continue to lightly stagger or make enemies flinch as long as the sweep can continue, and then trigger what we call a hitstop animation when your hit mass runs out (regardless of damage or stagger being inflicted). This animation however can be somewhat subtle depending on weapons. For example the Devil’s Claw sword first heavy attack hitstop animation is a slight catching/stopping of the weapon and then a bit more downwards continuation of the sweep.
Regarding presentation of all this data and stats, personally I’d love to improve it and show more in depth stats. But that of course hinges on the wider focus, plans, etc. of the teams and company. (And I want to stress that this is just my wish, and shouldn’t be taken as a promise.)