New Player Questions

Hello, I'm playing PoE2 and enjoying it, but having not played POE I'm finding some of the systems confusing and would like some help.

My build is below if someone wants to take a look, made in the path of builder site for POE2.

Here are some general questions I have (I'm a level 89 Gemling Legionnaire).

1. I've finished all the map quests for the Atlas tree, but there are trees to the side. How do I progress in the side trees?
2. Do mobs have inherent resistances? Is there a point in penetration for fire damage if mobs don't have extra resistances?
3. How do most players do their mapping. I generally boost every map and precursor tablet with a regal, is that what most people do?
4. For blinding and stunning mobs it looks like there's an icon on mobs that show the effect, is there a good way check these in game during an encounter? If you pause the game the screen with the icons are hidden.
5. Is there a noob player section/thread for questions like these?
6. What are some common things new players miss when building their character, similar to things like the radius jewels?
7. Does accuracy effect Molten Blast? I have some accuracy, but am not sure if it's worth it.

For those without path of builder, here's the TLDR of my stats:

-2656 health
-59% armour, 60% evasion
-capped resists
-Main attack is molten with scattershot, 8917 dps
-Maces are the 100% extra chance to daze

I Chose Gemling Legionaire because I wanted a build that was melee and ranged, and they looked versatile. When other weapons are released I'll likely try them out on this character and adapt the build.