Are there any good guides on how to optimize a build? This is the first time I've really gotten into a game like this, and I want to spend some time this weekend working on my build.
Honestly, I'd just wait a little bit before worrying. The game just got a massive balance patch on Monday so everything is pretty new. Talents were nerfed, health and armor pools changed, requirements for things to become active re-jigged. The builds that are online previously probably require minor tweaks or aren't as powerful as they were. The good news is that for PVE, if you've got decent gear, you should be able to play even un-optimized.
In general, for now, I'd say just try and find some gear with rolls that look good to you/your playstyle (do you like ARs/SMGs/LMGs/shotguns/rifles etc., do you go for headshots, do you play from cover mostly,, do you want to maximize crit chance/dmg, do you want to focus on PVE content and have lots of damage to elites?). From there, it's almost always more useful to have talents active than slightly higher rolls on gear whose talent isn't active because you have too many reds or too few blues. Basically, I'd recommend getting something you generally like, then trying to activate your gear talents with some minor tweaks to how you distribute your red/blue/yellow stats.
Division 2 has so many more variables compared to the first game, it's harder to achieve a min/max build. But it's a game that's more forgiving in that most builds can handle hard/challenging content.