>> "1. ForceCheckForUpdate contains a boolean param (recheck). What is the purpose of this flag."
The intellisense documentation tells you exactly what it means: "<param name="recheck">Recheck with the servers regardless of cached updates, etc.</param>"
You should never use that function. Just let the AutomaticUpdater check for updates. It's what it's designed to do.
"2. InstallPendingUpdate - What does this event imply?"
That's not a public event. It's a private function used internally in the source code.