I would put the last bit a little differently: they shed out that undercoat for the summer to stay cool. So it's not the undercoat keeping them cool, it's the undercoat being gone that helps keep them cool. And then of course they grow it back for the next winter.
Yes, combing or brushing out...
I'm a big fan of researching new ideas well in advance :)
That way I (or you) have time to think about the information, instead of trying to make a decision in a hurry.
You might call up one of the people selling them, and ask how they do in the summer. That would tell you about those specific...
I don't have personal experience with guardian dogs, but I have read enough about them to have answers to some of the most common questions.
They DO require training and supervision, especially at first. It's pretty common for the guardian dog to kill some chickens (or other livestock) when...