The official government program page and its published questions and answers. Commentary, news coverage and third-party summaries are not a basis for a financial decision of this size.
Go to the primary material every time
New programmes generate a large volume of secondary description, much of it written quickly and some of it recycled from earlier drafts of the terms. For a decision involving an irrevocable transfer, the only sensible source is the official material itself, read in full rather than skimmed for the headline figure. Note the date of each reading, because the terms of a recent programme can be updated without any announcement reaching the people who read about it earlier. Where the official material does not answer a question that matters to the decision, the correct conclusion is that the question is currently unanswered, not that a plausible answer found elsewhere can be relied upon.
The official source describes further USCIS instructions being issued after an initial payment step, so confirm the current version before assuming another applicant's checklist applies unchanged. Expect identity documents, civil records, evidence of the lawful source of the gift funds and whatever the official form requires for vetting, plus documents for the underlying employment-based process.