Is elemental sunder a thing? and if so how do you level it? I usually go life nodes down towards Art of the Gladiator, pathing dependent on bow vs wand vs Vaal Pact need etc. If you also like the game and want to customize your character to fit your personality, then be sure to check out U4GM.com, your one-stop, player-to-player PoE orbs buy destination. U4GM.com can not only provide best orbs in poe but also best solutions for all players, we will help you to enjoy more fun in this game.
● The flask nodes can be pretty solid too, especially since you'll probably need the +20 intelligence.
● The dual wield nodes are also a solid option.
● If you're really damage starved and unable to craft a good axe, you can grab some proj nodes and switch to Molten Strike with a single Wildfire, but I'd recommend against that. Just Rustic Sash recipe your levelling process.
● Not sure what you mean by Ele damage nodes. The Crit nodes around assassin tree will come when they do. The penetration cluster by Acrobatics is kind of ass. The pen cluster in the bottom right corner is solid, but usually comes after you get your key weapon nodes.
Sunder is a bad "elemental" skill (except for 100% conversion like avatar of fire) because it has 15% less attack speed and axes/maces have slow attack speed. If you're using flat elemental damage bonuses to kill things you want a fast weapon and a normal speed skill so you can take advantage of it better.
On the other hand % physical added as extra fire/cold/chaos damage is great because it's literally a percentage of all your damage so it scales with your phys damage.