Hi munzwurf,
Basically the rotation you have is good. I cast PW:S right before I'm about to cast Mind Blast on the mob so I have no downtime between my attack spells.
You can also try to cast Holy Fire as first spell as it has a long casting time and then -> Mind Blast, SW:P, Wand. If the mob is under 30% you can decide if you want to go for another Mind Blast or just wanding him to death. When you wand the mana regeneration will kick in after 5 seconds. Use this to have almost no or very small downtime.
When leveling the first 10 points should go into Spirit Tap and Wand Specialization. Further down until lvl 40 I went for shadow, some go for holy/disc for more dmg with Smite and Holy Fire, but I was ok with shadow. At 40 I reset my talents so I could get the Shadwo Form and then went for Wand Specialization again. Now at lvl 47 my rotation looks something like this: PW:S (before attacking the mob) -> Mind Blast -> SW:P -> Mindflay (1x-2x) -> another Mind Blast (if the mob has a lot of health) - Wand (till death). For lower mobs I stop at the first or second Mindflay and go for Wand. If I see that I'm about to oom I just go for Mind Blast -> SW:P -> Wand. Takes a bit longer but you have no downtime.
Let me know if you have any other questions
