Once the notary has estblished a nv, bvba or cvba the summary of the deed in which the company is established will be published on the internet. The notary takes care of the summary of the contract.
Then the company can get an inscription in the register of trade if it's aim is to do commercial transactions. There is also a register for civil companies, like for instance company with the only aim to own real estate.
If the comany is involved in VAT commercial activities, the company will have to make a request for the VAT number. This isn't either the job of the notary.
In the deed of establishment of a company, the founders often give a power of attroney to a person who works in the accounting firm which will take care of the accounting of the company. With this power of attorney the accountant can obtain the insciption in the register of trade and the VAT number.