I see you're going for the head, are you using a hammer? If so I can't really comment on ground patterns, as I mainly LS his tail and wings (and just pop his head on potshots, as opposed to going for the head consistently).
Regarding plate, what's rare on a given tier obviously becomes not-so-rare on the next, meaning you'll get plates in high-rank without trying. (Of course when you'll be drowning in pates you'll be wanting the high-rank set which requires ruby) Note that, however, if you're only missing one armor piece, you can often still jewel yourself up to get most of the set's skills.
On whether to skip los set, I dont know what skills are on it or what other sets you have, but if you're reaching the end of low-rank and you don't particularly feel too squishy on defence, I would tough it out for now and craft easy early high-rank stuff (wroggi, jaggi), which won't take long to make and might last you a while.