McKenzie, agree that there is a great element of 'he's just three'. My ds1 is 3 and a half, ds2 is 1 and a half. I have to say they get on amazingly well. Ds1 behaviour much worse now than a year ago. Find myself from time to time getting incredibly SHOUTY with him and it makes us both feel awful. However, I do often find that if I'm on top of him every minute of the day, behaviour wise, or if he's had a few punishments (2 minutes on his own, no pudding, that sort of thing) it does seem to improve his behaviour for a little while.
Have to confess, I find it very relieving to find that other people have similar problems with their 3 year olds.
Am thinking about use of star chart in vein attempt to limit my recourse to shouting.
Good luck - and with number 2!