These are included to block off the opening for the starter motor on racing engines.

I'm afraid it doesn't include the impeller. As long as the standard impeller is in good condition you can re use it on this kit.

yes ! you can see it in the top right of the picture (the black item)

yes to both questions, a competent mechanic can easily change the waterpump without splitting the engine but bear in mind it isn't really a job for a beginner