I'm on PC. Just finished main quest line in Wrothgar. Figured Hew's Bane would be the next logical zone. I've noticed that mats I find in Hew's Bane seem to be lower level though.

Personally, I would recommend that you don't play the storylines of Hew's Bane and Gold Coast consecutively. At least, not the TG and DB quests. They can get very repetitive if they're the only thing you're doing, so it's better to intersperse them with other content and each other. For example, if you haven't done Cadwell's Silver, start TG and DB, and then continue with Silver as you're doing the Reputation jobs. Once you've done enough jobs to unlock the next TG and DB quests, do those, then go back to Silver zones again when you're doing the next round of Reputation jobs. Constantly travelling between the Thieves Den, the DB Sanctuary, and the Silver zones to acquire, complete, and turn in the Reputation jobs gets old pretty quickly. (It would be great if we could acquire and turn in TG Tip Board jobs and DB Marked for Death contracts from Outlaws Refuges, then the travelling would be much more manageable.)

For the side quests in every zone however, I would recommend the order you suggested, as recurring characters will mention previous meetings in earlier zones if you've already done them.