N.D.
Pick a punishment and stick with it. ALWAYS I would rule out isolation in his room and opt for sitting in a chair watching what is going on around him for at least 5 minutes. Because of the PSD a corner or alone time might be what he wants. But consistency is the key. He needs to know what to expect ALWAYS. However do not use the same punishment for everything he does wrong. Save the one you pick for hitting or being very rude.
Also try to watch him and see what might be setting him off. Is he frustrated with a toy or task? Is he hungry or over tired? With most kids if you can identify the cause and nip it before they are overwhelmed, the tantrums will become greatly reduced. Then talk WITH him about how he might avoid the frustration the next time.