It would help if you knew what you wanted to major in. But in saying that, you don't HAVE to know.
Yes, 4 units/ semester is standard. Those four for sem 1 look good.
Now yes you do need to enrol for semester 2 as well, but you can always change these before semester 2 starts, so it is not a big deal what you choose - just choose something [although yuou will get limited choice in tutorial times, as they usually fill up fast].
What subjects you do really depend on what you want to major in, but looking at some of the major rules found here:
Bachelor of Commerce - 2010 Course Handbook - Macquarie University
i'd suggest doing:
ACCG100 [or106 if you definitely know you do NOT want to major in accounting]
ECON110 [you're already doing micro so might as well do amcro, plus this will coutn towards an applied econometrics, eocnomics, finance, +other majors]
STAT170 [(or PSY122) - statistics, i believe, is useful - plus this will coutn towards an applied econometrics, eocnomics, finance, +other majors]
and an elective of your choice [perhaps a people or planet unit - refer to
http://www.handbook.mq.edu.au/2010/Units/PeopleAndPlanet]