A dated printout of the official page and FAQ, identity and civil documents for every included person, a complete source-of-funds file for the gift, a record of all prior U.S. travel and immigration history, and preliminary tax advice. Expect further instructions from USCIS after the initial submission.
Prepare as if the instructions will get stricter
Hypothetical example: a Haldimand County retiree begins the Gold Card process from the official website and finds the initial form asks for less than he expected. The right response is to prepare more than is requested, because the official process describes further USCIS instructions and supporting documentation after the initial application and fee. Assemble passports and citizenship documents, marriage and birth certificates for the spouse and any included child under 21, a chronological record of previous U.S.
entries and any refusals, and a source-of-funds binder covering the full gift: the business or farmland sale, investment account histories and tax returns. Save a dated copy of the official page each time it is consulted, since the terms are described as current rather than permanent. Obtain a written note from a tax adviser on how the gift will be treated in both countries.
Keep the eventual EB-1 or EB-2 stage in view: the applicant will still pass through consular or adjustment processing with medical examinations and admissibility review.