There are students who would actually work more than the 20 hours a week limit, of course illegaly. Now, even though I have never heard of any student being kicked out of the country for working more hours than they are allocated, its a risk that most students will not take. So suit yourself.
Also, don't forget the fact that you only get your work permit after 6 months of full time studies.
Now, in the summertime, You can work full time without limitation. Some students would do 2-3 jobs during this period to rack up some money.
Most importantly, to answer your question, it really depends on what university you are in and what kind of personality do you have. if your uni charges 20K per semester, then just forget it. But if your uni charges 3-6K, per semester, then its doable.
Also, if you are the kind of the person who needs to keep up the appearances, or worry about what your friends might think when they see you working at hot-dog stand, then again, have someone else pay for your tuition fees.