Don't think I'm going to be much help, but from my understanding;
1. A Commerce degree for HR will make you more competitive, but is not 100% essential. (EDIT: A degree is still often a requirement for management HR positions.. I just mean't you can also get in via other degrees like Arts etc..)
2. Depending on the organisation (and from my personal experience) HR management tend to do some overtime. 45+ hour work weeks are not that uncommon.
3. According to my lecturer (did HR subject), there is definitely work in HR.
I'm not too sure about the occupations you mentioned (psychologist, physiotherapist, dietitian) being crap paying, but you're right - there's probably more work in HR.