Who should I tell about the sale process within my organization and when?

As a rule, tell only those who need to know.  Certainly, you should involve your outside accountant and legal counsel.  In terms of your staff, if you think you cannot go through a sale process without the assistance of a key member of your staff (typically a finance/accounting role), you should consider whether that person can be trusted to keep the process confidential.  And you should only involve others when it becomes obvious that you cannot effectively manage the process without additional assistance.  While we have never had a “leak”, and even in the event of people suspecting or finding out about a transaction it can be managed without serious consequence, best practice is to limit knowledge of the sale process.