It depends on your class, how sustainable you are in combat, if you play with a friend, PvE vs PvP, etc. I play a Templar, with a lot of self-heal options, so I generally never found myself in need of using potions. I leveled up with my sister, a Nightblade. That made content a heck of a lot easier overall, so upgrades weren't nearly as pressing an issue. We did PvE content exclusively.

First starting out, I swapped in found/reward equipment. Once our crafting skills were sufficient, we generally replaced our armor 1 to 2 times per Tier (i.e. we'd get Steel when it was first available at 16, then upgrade around 20-22, if we didn't skip the upgrade entirely). For weapons, those were replaced more often, when they started to "feel" ineffective -- but we also improved them to Blue or Purple quality to make them last longer. Armor we usually stuck with Green quality with the rare Blue upgrade.

Veteran Levels we replaced armor every 1 to 3 VR levels, and weapons every 1 to 2 VR levels. Fortunately, there was a lot of time to collect materials for Veteran content (provided you are questing and not grinding XP). Weapons we made Purple, armor Blue.

A lot of it is going to be a "go by feel" kind of thing. If you are working on your crafting skills, you'll have an easier time fiddling with it. If not, and you are tracking down a craftsman every time you want an upgrade, this will probably feel like more of a hassle.