I hope to apply the Tooling Gelcoat tomorrow (Tuesday) and then on Friday apply the Coupling Coat, followed by the Tooling Resin. Will this be OK?

That said, the Unimould tooling gelcoat should be an air-inhibited cure, so it should remain open to bonding for a good amount of time. However I would suggest that your time frame will be too long. Not only does it leave the surface vulnerable to collecting dust and other contaminates that will affect any mechanical bond, but 72 hours is a long time for the gelcoat and it may cure to a stage where it is no longer open to bonding.