I'd advise against using the gems. Save them for boosts/builders.
As others have wisely pointed out, de storage and drill should be your building and upgrading priorities when you get to th7. Once they are set up, use giant/archer/goblin raids and hit bases in gold 2-silver 1 with 500+ available de. Shoot straight for the storage. You can get the 10k quickly for the king, and then some for his upgrades and the new dark troops you'll get.
Good luck.

