When I started (in 2004) I don't think we had flexible engineering so for Electrical engineering so we had a pretty much fixed plan for the first 3 years on what subjects we need to take. In your case now it seems you only have 5 subjects in year 1 that you must take and the other 3 are electives. So yes if I am in your position I would take some core commerce subjects like microeconomics...
Also yes you can do the subjects in any order you like, you just need to keep track of what pre-requisites you will need in order to do the core subjects for next year. When I started I was essentially following the electrical engineering plan for the first 2 years. Then I went into eng/comm degree (via UAC) and started my first commerce subject. After that I overloaded a few times and just ignored the official program so I was doing my engineering core subjects and filling the rest with whatever commerce subjects fit into my timetable
. If anything it makes things much easier if you mix commerce and engineering subjects in the same semester, it gives you less hours per week and allows you to have more time to do other things.
In the end even though I overloaded a few times I decided to leave it to 5.5 years as it would have been too hectic to do my thesis while overloading. So now I only have my thesis and one more commerce subject I need to do before I finish...nice relaxing way to finish...if I didn't also have to work part time lol.