New player with some questions

Me and my friend play a lot of Diablo and PoE, but we're having a hard time ever since we hit act 4 of this mod. I'm playing a make shift Electrofield Assassin build but I'm stupidly squishy even though my resists are capped. When I'm not in fear of dying i'm almost pulling my hair out trying to figure out what element the next mob isn't immune to, I don't like having to always change my abilities when I only have 1 button to cast with. Are these issue that everyone playing this have to deal with? if so then what is the toughest build that I can start out with to have a more relaxing leveling experience?

Totemmancer is probably the safest most powerful build. Can rape the game with mostly honorifics . Traprat is also rather safe. Both builds tend to get a bit boring later on tho but yea try one of those.There's a few more like unholy caster paladin, but those 2 require much less effort for high reward imo.

I actually made a Unholy Caster to try and yes it's way less stressful to run with.

You only have one button to cast with? Do you know about quickselect or whatever it's Called?

You can quickly switch between skills by hovering over the skill in the skillselection and pressing F1-F8 and when you press that button that skill is automatically selected so you can quickly switch between skills.

That works both for rmb and lmb