Schools & languages:what to choose? (Brussels)

Hi to all and especially to mums and dads,
In January we will be moving in Brussels with our 3,5-yr-old boy and we would like to send him to school. He is fluent with greek and italian but doesnt speak a word of english or french.
First of all, I would like to ask you if you have any experience on this "melting of languages" and what kind of probems, if any, you faced during this process of your kids' learning 2 more languages. How long did it take to manage in both new languages?

Another question risen, closey related to the first, is what scool to send him to. A french-speking one, an engish-speaking one or even a bilingual (en-fr)?

Thank you for your valable feedback