I don't think you need to bring anything on the first day -- like MarieZug said, wait for a special occasion. As for the probezeit, I think they do that more in Germany -- I never saw it here.
well i guess it depends on where you work? i work at the university and it's quite common (and more than welcome!) for people to bring something on their first week here. and on birthdays. and on whatever other occasion!
Cake and croissants always go down well in our office no matter what the occasion is....
I would suggest you wait until the end of your probation period. You'll have enough to worry about on your first day without the added stress of catering! Each company and the people that work there are different and have different expectations on if and when you should bring cake in. Where I work its usually birthdays only, or if one of my team (i.e. one of us girls) gets bored and bakes at the weekend we take in the left overs for our team mates (the boys).
Lead from the front; if there are only four people, you'll at least get off on the right foot being friendly and considerate. It's a nice gesture. Prince Edward brought a box of tea bags on his first day, knowing he'd be the tea boy...
Ah well if it's only 4 people take something then. Small companies tend to be a bit more ralaxed, and less stuffy than large companies. It'll help break the first day ice.
If it was a large company I wouldn't bother. In a large company you'll probably end up doing an induction day and never end up meeting those first day people again.
On the other hand, i will be starting next week with my new job, the office is so spacious with approx 500 sqm split over 3 rooms, over a hill & over looking the Neuchatel lake, the only problem is i'm the ONLY one there, can someone drop by & celebrate my first day with me PLZZZZZZZZZ (You can bring with you whatever you fancy, i don't mind anything really)
Nothing the first few days except a pleasant personality and an ability to make people feel comfortable with you. After a 2 or 3 weeks some home made cookies, or warm croissants