You can't do psych for your combined degree unless you are in Arts-Psych Law.
It is recommended you do as many different units as you can. So you can do the rest of the ones you mentioned, along with anthropology, sociology, politics, languages, cultural studies, WHATEVER!
But from second year you'll need to take most of your electives in your major and third year..all of your electives from your major.
A good way to do it is to a) Buy the uni handbook and b) Think about a possible major (e.g. english) and make sure you have the necessary first year and second year units. I think there's only 1 first year english unit that is a necessary 2 get into second year english units from memory.