do you recommend working and studying at the same time? How are you finding it? Does it get in the way of your academic performance?
A lot of people at uni have casual/part time jobs. How much people work depends on various factors - the extent they need the money, how much effort they want to put into their studies (and how much they care about their marks), what other things they are doing apart from work and uni (eg. involvement in clubs and societies, student politics, volunteer work, family commitments).
I worked 2 days a week last year in an office job, but felt that with the pressure of work plus a lot of time I put into a uni club as well as still wanting to do well, that it wasn't worth the stress of doing 4 subjects (I also wanted a vague kind of social life), so I dropped down to three uni subjects a semester. Whilst I wouldn't normally put work in front of uni, this was a job which gave me experience in the profession I want to go into after uni, as well as needing the money. In previous years I would work anywhere between 8-14 hours a week (check-out-chick).
However some people do perfectly fine working 2 days a week - and some people will work more than that. It is really up to you, what you think you can cope with, and how well you want to do at uni.
edit: having some kind of job in uni is always good - it means you have something to put on your resume and many jobs value you having work experience - it doesn't need to be anywhere near the area you are going to work in - however even working at maccas shows you have dedication, organisation skills, happy to give something a go and can deal with people.