Hello
I am currently a second year Environments student. When I entered the course I was going to do Architecture, but I have swayed my interests towards the Urban Planning & Design major instead. The degree requires you to do six core subjects (out of 8 to select) in your first year: Natural, Reshaping, Constructing, Designing, Virtual, Mapping, Urban and Governing Environments. It gives you a very broad palate of options, so it will be very hard to pick your major if you enjoyed all of them
In terms of electives, with the Architecture major you get three electives, as well as your breadth subjects, which you can actually choose from the same faculty if you do Environments (unique to Environments in the Melbourne Model). I do, however, recommend doing breadth subjects in something completely different because it refreshes your mind.
Here are some links that will help you get a feel of what subjects are being studied:
For all of the subjects:
Architecture : Bachelor of Environments : The University of Melbourne
For electives:
2010 Elective Subjects : Bachelor of Environments : The University of Melbourne
For breadth:
https://handbook.unimelb.edu.au/faces/htdocs/user/breadth/BreadthSearch.jsp
Hope this helps!