Key to victory: Use crystals to craft x2 items. This is literally all it takes. Don't worry about gold or anything else, those things are trivial once you start to craft. I was about to go from difficulty 10 straight to 20 in five minutes, so don't worry about grinding, just craft x2.
 "Realm Grinder")
 "Sky Quest")
If you hover a building button or a royal exchange button, you should see how much it would cost to buy 10 or 100.