Steve Gorak:
I may be wrong, but that's why this is a learning process for all of us. But the way I read it, there may be some issues with your character sheet (outside of wanting three rods of corruption

).
In one of their handier endeavors, Wizards has developed the
D&D Compendium, and that's what I'll be quoting from here.
Arcane Initiate [Multiclass Wizard]
Prerequisite: Int 13
Benefit: You gain training in the Arcana skill.
Choose a 1st-level wizard at-will power. You can use that power once per encounter.
In addition, you can use an orb, a staff, or a wand as an implement when using a wizard power or a wizard paragon path power.
You seem to have chosen two: Scorching Burst and Thunderwave.
Also, Arcane Implement Mastery--in this case, Staff of Defense--is a wizard class feature. I don't read where the Arcane Initiate feat grants you class features of the wizard class; it only allows you a per encounter use of an at will wizard power (and the ability to use a wizard implement to deliver it), and grants you training in the Arcana skill.
So basically, the way I see it is that you have two too many encounter powers: one being the Staff of Defense you have listed, and the other being either Thunderwave or Scorching Burst.
Thusly, I used your eldritch blast to take out one of the hobgoblins instead of the scorching burst, since I didn't know which you wanted to keep, that or thunderwave.
If I'm wrong here, please don't be offended. As I said, we're all learning here (unless one of you is secretly a 4e designer or something, in which case you need to speak up and educate us all!). I'd appreciate feedback from the rest of the group as well so hopefully we can get all squared away. Sorry it's taken me this long to notice it.