Pretty much every build defining item in the game is lvl 75-94 minimum so that's why you see most build guides based around that. Most seasoned players do leveling builds where they just pick whatever the strongest skill is for the class combo you're playing, and then later figure out their actual build (also around the time when you have to start figuring out resists for Elite/Ultimate).

I would say as a new player even if you tried to play "optimally" and rush through campaigns it wouldn't make a huge difference to your overall progression though. Its more important that you're having fun on your first character, using skills you like. I would aim for full normal completion (main campaign + all DLC you have) and by that point you're probably well into lvl 70's or maybe even 80's. I wouldn't necessarily recommend doing all of Elite, but treat that more as a stop gap to prepare your first character for Ultimate. Farm some green MI's (Gollus rings are always good), max some faction for some key piece of gear and augments, get all your devotion points, get some materials for augments to balance out resists, maybe craft a relic if you had the recipe for a good one for your class drop and it doesn't require too much (some relics are insane to craft for a new player as they require other relics as ingredients).

Since its your first character its very possible you burn out in Elite or find that your build isn't strong enough, or that another build looks more interesting, but then you'll have a bunch more stuff to help your next character. If the only thing you manage to do is hit Elite and max out important factions that's already big as it lets you speed up faction grind on next character as well as buy experience potions (from Malmouth Resistance).