The minimal capital of a 'nv' ('sa' in French) is 61.500 euro

This is the absolute minimum. The is now way to go lower if you want the establish this kind of company.This 61.500 euro should be available at the establishment of the company.
(Source: article 439 Company Code)

There should be an attestation of a bank that this sun has been deposited on a bank account. This bank account should be a bank account of the company. The capital of the company belong to the company. Once the company is established, the company can use the sum of money.