Thief stone and Shadow stone work for magica and weapon crit/damage. Thief is likely your best bet.
5/1/1 can be good to make sure you level up all skill lines in case you want to try a different play style or eventually use the undaunted passives. It really doesn't make a huge difference anyways until you have the skill points to get all the passives. So using all 3 armor types to level is a no-brainer to do. Once you get to max level, 5-7 light will be best for dps, although I usually have a set of heavy because I just find it is better when I want to solo or even tank a dungeon.
Dark Elf would also be a quality race choice as you could use a fire staff and use elemental blockade which has a nice cast time relationship with twisting path for two good ground AOE drops.
Key Skills:
your main single target spammable is either Strife (Swallow Soul) from the Siphoning tree, or Force Shock/Force Pulse from Destruction staff. Force Pulse will do more damage, Swallow Soul will heal you and cost less magicka. If you're going OOM a lot and/or having trouble staying alive, use SS, otherwise use FP.
Elemental Blockade w/fire staff + Twisting path - main AOE damage
Siphoning Attacks is obvious for resources.
Assassin's blade/impale is great for execute, and works well to do insane damage when paired up with the grim focus skill and the quickly recharging death stroke/soul harvest ultimate from that tree as well.
Annulment/harness magicka from the light armor tree is gonna be something you'll want to cast a lot to keep yourself alive.
I'd say those, In my opinion, are the "must have" skills. Unless you want to heal, I'd see how well Swallow Soul and Harness Magicka keep you alive before worrying about resto staff but it never hurts to have that skill line levelled just in case.