I understand, OP. My husband is the same way, and I'm going to tell you what I told him. It's your game. If the idea of moving to another zone before completing the Hinterlands stresses you out, you have to do what makes you comfortable. You may want to finish the quests in the middle of the map before moving toward the south, the northeast, or the far west, but by the time you've cleared the Crossroads quests, you should be level 8-11 anyway, so the quests in the south and the far west won't be too hard for you. But definitely, definitely wait until you are at least level 12 before entering Lady Shayna's Valley. There are enough quests in the Hinterlands to reach level 12.
You also need to accept the fact that you are going to be overleveled in other zones. All that means is that the creatures you encounter will not present much challenge for you and that the gear you find will be weak. You will never be locked out of quests because you're too powerful.
When I play, I go to Val Royeaux as soon as I have 4 power points, but that's only because I want to pick up the companions that aren't available before that. Once I have everyone on board, I go back to the Hinterlands and clear it of everything that doesn't breathe fire before making the choice between In Hushed Whispers and Champions of the Just. Yes, I'm horribly overleveled by that point, but who cares?