take time to wander around the Grand Place there are heaps of restaurants off it that offer some fab food.
The antiques market in the grand Sablon on Sunday morning is well worth the trip, bring some spending money for it! You'll find some great stuff, and the prices are reasonable with a wide selection of stuff. IF you do go to the Grand Sablon there was a lovely restaurant there that did a nice brunch on the sunday morning, can't remember the name, but its more or less opposite the church, and had a bakery/coffee shop to the front, with the cafe out the back. I remember having a lovely vegetarian brunch, but I dont' think it was vegetarian only.
The royal army musuem is well worth a visit, its over by Schuman metro station, and its under the Belgian version of the brandenberg gate (sorry can't remember its real name). Considering most european conflicts have taken place in Belgium, from waterloo to WW2 its got some excellent stuff on show - and my hubby really loved the selection of military planes and tanks!
Avenue Louise would equate to Grafton St in terms of whats on sale there, so I'd suggest if you want to shop check out Nieuwe Straat / Rue Neuf, its about 5-10 walk from grand Place and that more along the lines of Henry St!
Enjoy