My gut feeling is
A) he's 4, 4 is tough on parents.
B) he's very ready for school, all the ways it will extend him.
C) he's normal (mother of 3 boys here, so I must be wise, HarHarHar...)
personally, I don't think 'letting anger out' is the right approach. I recently read something I've long suspected, if you hit a pillow to get your anger out it doesn't make you less angry, it gets you worked up.
Anyway, I would make sure he's fed frequently enough, and try to make sure he's tired out in a relaxed way, but not over-tired (very tricky balance, i find).