For me, the mage seems to be the most hardest class in order of planning the spending of skill points.
In regards to the tempest, its only the daggers i have a little trouble figuring out how much i want to invest in a skill tree.
Hopefully i can ride a wyvern and role play that's where i get the poison for my daggers.
Hmm. I don't find it that tricky.
Obviously I haven't played the game, but it would seem less difficult this time around.
Defensive Mage: Max out both Spirit and Knight Enchanter specialisations. Keep your allies close, defend them with your spells and support the front lines with healing and a bit of melee combat. (Not the bulk, because as demonstrated you're still squishy). If there are any points left after maxing both skill trees, pick an element and dump the rest of your points there.
Offensive Mage: Pick and element and max out skill tree. Then pick either necromancer or rift mage then max out said tree. Dump the remaining points in whichever tree you want. Pretty easy. Keep back, let other party members tank and deal hefty damage.
Defensive/Offensive Mixture: Spirit + one of the elementals + some specialisation ideas. Okay now this third build might be tricky. It's pretty versatile but deciding what skills to pick and what skills to ignore will prove challenging.
If in doubt, pick one party member to be a defensive mage and pick one party member to be an offensive mage.
Vivienne as defensive and Dorian or Solas as offensive.
Then pick a tanky warrior and rogue (archery or dual wield).
There. A traditional warrior, rogue, cleric and mage type setup.