The application and mailing instructions are very clear from the USCIS website.
(734) 369-3131. This communication does not establish and attorney-client relationship with the Law Office of Michael Carlin PLLC or any individual member of the office. Confidential information should not be sent through this form.
While it used to be possible to file I 130 in Belgium this is no longer the case, as there is no USCIS office in Belgium. You need to file at the Chicago lock box http://travel.state.gov/visa/immigrants/immigrants_5254.html
On question 22. On the I-130 you will indicate Belgium as the designated consulate.
Please consult with a family immigration attorney
The US. you used to be allowed to file in the foreign country if the US citizen petitioner was legally residing there, but that rule changed not long ago. You don't notify the consulate. The government does so. I think it would help you to have an attorney who knows all the different steps and what happens when.
This reply is intended only as general information and does not constitute legal advice in any particular case. This reply does not create an attorney/client relationship.