Commit the funds before applying, but structure the commitment so a refusal does not destroy him. That normally means an executed agreement with the money placed beyond his control except on the immigration outcome, rather than an option, a letter of intent or a deposit he can simply take back.
Committed first, then adjudicated
The order feels uncomfortable because it asks a buyer to be exposed before he knows the answer, and that discomfort is exactly what the at-risk requirement is testing. The workable middle is an agreement that binds him, with escrow conditioned on the classification alone. Around that decision sit several other timing questions.
A season in this trade is short, so closing in the autumn and applying over the winter usually beats closing in June and losing the year. Equipment purchases and lease commitments made after closing strengthen the file, so keep the receipts. Renewals and extensions are decided on the enterprise as it then stands, which means the second application is examined against real trading figures rather than against the plan, and a business that never grew past supporting one household will face the marginality question again.
Confirm current requirements from official sources before any money moves, since program details and fee amounts are revised from time to time.