Brand new to the game, about 2-3 weeks into the game and feels like I'm now hitting a wall...

Are there any sort of progression/team building guide I can read through?

Also it does seem that the general consensus is to have one main element team to work and a backup in for the element your main team is weak against for the game... I would imagine trying to build a team for all 6 elements is something you do later in the game?

Reading the forum through, it seems that the community prefers stacking assault weapon skill than defender. In this case, how do you get enough HP to ensure raid boss doesnt one shot your team?