I'm not familiar with Mega Man, but I am very familiar with 5E's cyberlimb rules.
They're unfortunately very complex, but it sounds like your GM is familiar with them and simply using them as presented. (see pages 455-457 of the core rulebook)
From a character design standpoint, if you want to do 4 cyberlimbs (again, I don't know if that's what you're going for when you mean Mega Man) you'll be challenged by two constraints: essence and resources. Now that's true for any heavily augmented sammy type, but limbs are so essence-intensive that they don't leave much for the other things you'd reasonably want, such as initiative boosting 'ware. Since cyberlimbs give Capacity, use that as much as possible whenever possible to get cyberware for "free" at least from an essence standpoint. For example, Wolverine-style retractable cyberspurs cost 0.3 essence, but if you build them into an artificial cyberarm instead of essence they cost 3 points of that limb's capacity limit instead. The biggest challenge is there's limits as to what sorts of things you can install into cyberlimbs instead of counting against your essence. Again some things you'll likely want do not come with an option for capacity cost instead of essence cost.
The trickiest thing of all with regards to cyberlimbs is their stats don't count towards calculating your Physical limit. Even if you get to use your giant Agility and Strength ratings for an unarmed attack with one massive cyberarm, if your natural physical attributes suck you're still stuck with a low Physical limit for that attack.