Yeah the switching between elements is a hard thing to do properly. With a spear this is getting even more harder considering the buffs and utility you get to maxime your damage and handle your defense and the same time.

Ranger might be my second pick right after Ele. The theme around Petsprits as weapon are kinda cool

That was exactly my concern. Some effects look so overloaded that crashes might occur easily.

I feel like that celestial gear is insanely usefull when doing open world content like events or general exploration. In fact endgame content like raids requires a different type of gear (mostly in raids or fractals or strikes) If you want one set for open world AND pve instances celestial gear would be a bad choice. If I were you I would take general condi or powergear instead.