There are no differences between physical damage and elemental staffs besides the type of damage they deliver. They both deal ranged damage unless attacking an enemy nearby and both can be buffed by elemental weapons.
Just some things to consider:
- If you want to melee with a staff, you'll have to manually move into melee range or wait for the enemy to get closer.
- Mage auto-attack dps is considerably weaker than rogues and lacks the area attack and self-buffs of warriors.
- Most of their damage/utility comes from casting spells.
- Mages tend to be more squishy than warriors/rogues even with sustains (less armour, damage resistance, defence, decoys)
If you're still willing to play such a build:
- Pumping magic to 100 before moving to dexterity will always be best dps-wise. Equipping +critical damage/chance or +%elemental damage will also help.
- The mantle of the champion doesn't require that much willpower (18 willpower), so you shouldn't need to get any willpower if you pre-buff (equip +attribute/+willpower gear first).
- Force mage will only be useful if you are willing to cast spells. The 'unshakeable' passive is largely unnecessary post-patch, so the main advantage would be destealthing assassins and crowd controlling groups of enemies.
- If you stack lots of sustainables, blood magic will probably be necessary to cast spells.
- Sustainables in DA2 can make you more durable, but not to the same extent as in DA:O. Even with rock armour and arcane shield you will still take a lot of damage in melee.
- Healing aura will add the most durability, but only if you have a high base health to start with.
This leads to two builds:
- Spirit Healer "Tank/Buffer": Focus on constitution. use combination of healing aura, rock armour, and arcane shield to tank damage. Add some utility to the party via sustains (heroic aura, elemental weapons etc). In theory, the mage could be next to invincible, especially on lower difficulties. The downside is crappy damage/attack-rating, and very low mana to cast spells.
Due to the low threat generation, having a rogue redirecting threat towards your mage with goad and armistice will probably be necessary.
Speccing into bloodmage will allow switching between a caster/utility mode (haste, healing, debuffs, crowd-control) and adds some extra damage/durability via Grave Robber (deals spirit damage based on max health, which should be massive).
- Normal build: If you're willing to cast a few spells, it's probably possible to go 'melee' with a standard dps-orientated mage build. If you freeze them with a cone of cold or drop a gravitic ring (and ideally a firestorm) on a group of enemies, you should be able to flail at them with your staff for a while. Without spells/crowd control it'll be pretty much impossible to fight a group of enemies with melee auto-attacks.
That said, I haven't had much experience with lower difficulties, so perhaps a melee approach could still be reasonably effective and durable on casual.