That leaves one @will (since human) and one lvl 5 daily power. Since many of the powers I have above are single target powers I was thinking of adding some area powers. Currenlty I am thinking Blazing Starfall and Suns Illumination (though I think the Acid Orb would be quite useful as well). Any ideas?
You're only going to use Acid Orb over Chaos Bolt in one of four situations:
1) The target's Ref is so much lower than its Will that it's worth giving up a ~30% chance of hitting at least two targets (That percent assumes you hit on a 10 or higher). You also need to know that the target's Ref is much lower than its Will, which may not come up depending on the DM and game style.
2) You want to hit a target 11-20 squares away from you. Most ranged attacks need to be within 10, and many need to be within 5, so in most cases this won't come up as 10 squares is already behind the rest of the party. But in certain campaigns, this could be useful.
3) You get granted a free basic attack (or are granted a bonus to your basic attacks). If you don't have acid orb that attack is wasted. However, for most parties, this won't come up much if at all (You can make it come up with itemization -- with, say, Eagle Eye Goggles or an Impaling Dagger. The latter is a bit cheesy.).
4) You are fighting something Psychic resistant (a rare resistance).
You will use Blazing Starfall over your other At-Wills in one of two situations:
1) You are fighting undead.
2) You want to make an AoE attack without getting close to your enemies.
Personally, I think the situations where you want to use Blazing Starfall come up much more than the situations where you want to use Acid Orb, but it definitely depends on your campaign. And if you're not interested in Blazing Starfall, you can itemize to make Acid Orb be better than Chaos Bolt in certain situations (but probably still worse in generic combat).