The glyphs can be very hard to find when on legendary as you are getting shot and blown up. So the bets bet would b to finish all the enemies in a certain area, then have a thorough scan through the environment, checks under rocks, on the ceilings, anywhere where 343 could hide the glyphs. But what most people tend to do is just Use Youtube sadly, and that ruins the fun of the find.
If i remember correctly, Requiem Archive I rewards you with Raider, Shoulders, Torso, and Chest. and of course the Raider Emblem. Requiem Archive II rewards you with the DSTT Skin for the previously unlocked Raider Shoulders, Torso, and Helmet. And then Section 3 Rewards you with 4 unique and cool-looking emblems, the glyphs for these ones however are even more harder to find than the ones required for Archives I and II. There are 4 Emblems to unlock with combinations under the Section 3 Archive, as far as i am aware.