It's always worrisome when our little ones are having any procedure that requires anesthetic, but I'm sure your little Wally will be just fine. My Ruby was just at 3lbs when she was spayed and had 10 retained baby teeth removed. Reno is like your Wally, was neutered at 16 weeks and had retained baby teeth removed later.
I've never had anesthetic alter a dog's personality for any longer than a day or two. Then it's just that they are sleepier, less energetic, not a true personality change.
Good luck and please post an update and let us know how he did.
