The evidence any employment-based immigrant classification would require: identity and civil documents, the business and professional record, tax filings, and a clean account of the source of the funds. Certified English translations are required for documents in another language, so those can be commissioned early.
Prepare for the underlying category, since that is what will be adjudicated
A recent program will have procedures that evolve, and preparing paperwork against a form that has not settled wastes effort. Preparing for the underlying classification does not, because the requirements of the existing employment-based preferences are stable. For Bertrand that means assembling passports and civil documents for each family member, marriage and birth records establishing the relationships being claimed, and the professional and business record that would support the classification: corporate registrations, contracts, financial statements, and tax filings across several years.
The source of the money should be documented to the standard any government enquiry would expect, tracing it from the business that generated it. Any document not in English needs a complete certified translation, and there is no reason to leave those to the end. What should not be prepared in advance is a payment: the processing fee is nonrefundable, and re-verifying the official terms before transferring anything is part of the process rather than an afterthought.