Sadly, I have to work the 5th and the 6th.
Would have been nice to welcome a fellow forumite to my barrio.
From the photo's I've seen of yours, (good work, by the way) I think you'll be happiest where people congregate.
The rue Neuve is the middle class shopping street, Louise is where affluent people shop. You'll find the african quarter near the Porte de Namur - it's called Matongé.
Of the central pentagon that forms the old town, the west and north is more upscale, peppered with government buildings, embassies and office buildings, the south and east is more popular, poorer, more diverse. You'll hear little french and even less flemish, lots of moroccan, turkish, polish, and in the centre of town, the eurocracy goes to ball, and you'll hear everything from danish to greek, from german to spanish, and never forget the italians.
At the Place du Jeu de Balle, there is a second-hand market every morning of the week.
There used to be a forlorn russian there, half hiding between the stalls with a plastic bag full of zorki's and feds.
I won't go on. Have a nice day in my hometown, don't start drinking the beer too early, it can be treacherous.