The information you have provided seems to be very helpful. I will give it a try indeed.
I have already contacted the mentioned archive in Brussels and I'm on a progress to reproduce a file regarding a family relative. Do you know if it can be sent by e-mail or just in hard copy?
In addition, I found on FamilySearch an immigration documents from Antwerpen, 1926, that with a careful guess I belive it also related to my family. What databases do you recommend for such documents?