im not sure if i should spec darkness or runecarving for xp. any advice or am i totally wrong and spiritmaster are more needed in pve/pvp?

Darkness is better.
You do better damage with debuff-dd + normal dd than with the rc dd.
You are useful for melee groups because you have the strongest dmgadd of the realm.

where are good lvl spots for runemaster? (lvl 5-50)

I xp'd mostly in DF and mid-dungeons (nisse, vendo etc.) - I prefer solo with rc-spec (bolts) or grp with dark-spec (damadd), though dark works nicely for solo aswell..

I assume you are past the first 20 levels by now.

DF is always a good choice, I agree to Zubasa. If it is closed go to Vendo until mobs are too low, then get a group and go to Spindelhalla, which is nice until late 30s. Once you hit 40 just get Agra groups.

Solo you can start Spindel at 33, the low mobs are orange by then. But things are getting slow from then on.

I do not like Malm too much, but that is just personal taste maybe.