as for earth crystals, i dont think there's actually an easy way to get them. they dont go up for sale ever, unless capcom release a patch to upgrade the store like they did with 3U, but tmk, there's no such patch in the Japanese version so far, so I doubt one will come (which sucks). the easiest way to get them is to make an armor set with all the gathering skills and then go to sunkers hollow or sth and mine the **** out of the mining spots, and bring along palicoes with the treasure/gathering skill so they can help out, too. then just bring a farcaster so you can easily teleport back to the base camp once you've mined the area clean so you complete the quest quickly and then go again. it's possible to get like 60+ earth crystals per run from this method, which only takes about 5-10 mins to do so it's really not that bad.