>>96695568
>>96704531
I agree that four is about right.
Piloting = maneuvering in difficult circumstances, evading attacks
Close Combat = fighting with melee weapons or the mech's body; includes blocking
Gunnery = attacking with ranged weapons, including projectiles and beams
Tech = sensors, comms, ECM; may include guided missiles

Specialization within each field can be added on in whatever fashion suits the game system

>>96700410
Going to depend on the system.
Maybe every unit has some basic Defense score that is rolled against for an attack. More active defenses like dodging, blocking, etc. require spending or reserving an action. Blocking lets you interpose a weapon or shield between you and a threat. Your beam saber catches and deflects theirs, or your shield intercepts their bullets. Maybe it just passively adds an amount to your Defense score. Meanwhile, Parrying could be a roll-off between attacker and defender (presumably in melee), pitting skill against skill. If the defender beats the attacker by enough margin, maybe they get to deal some damage as a riposte.