Limited host header redirection & question about irule statements processing order

I am answering some of your questions:

HTTP_REQUEST & HTTP_RESPONSE are two different events and can be used within a single iRule or multiple iRules. I would recommend using it within a single iRule.

HTTP::respond is an action that is utilized within the HTTP_REQUEST event and not HTTP_RESPONSE.

Personally, I would recommend using the "event disable" sparingly. Instead of using multiple switch-statements with event disable, can you try using if-else-statements ? Using if-else conditional statements such that the specific matches exist at the top of the iRule will help you to stay away from the event disable statements.