well one of the things you have to decide, is where to set the baselines.
for example if we say that the human soldiers wear ablative /flack equivalent armor (or just flack) that sets a reasonable base to build the rest of the armor off of. of course that means that mjolnir armor (the Spartans powered armor) is at least a PA:L suit. which is actually pretty accurate IMO, and if you want to incorporate the "shields" there should be rules for that as well.
personally the simplest rules for "shields" is to give them a hp equivalent, an absorption rate and a recovery method
IE the Spartan shield has 20 hp equivalent, recovers 0 hp per round when under fire but on a "shield check" recovers mos shield points or something similar.
of course the covenant use a lot of energy weapons, with a notable exception being their needlers, which are much like needlers in MechWarrior, with the exception that the cov needles will detonate a few seconds after they are fired
