Strategy question on achievements

Goliath incarnate - How does anyone get this? By the time you get assault mechs there's hardly any light mechs on the field?

Quick fix - Also how the hell do you get this?

No Small Feat - Does this have to be done all within one campaign run? Chassis become too light to be viable so quickly. With light mechs there are not enough assault mechs to destroy and vice versa. The two I have completed (Shadow Cat and Mad Dog) I had to run entire stars of the mechs to get the milestones.

Mauler and the Viper - Also how the hell do you do this one?