My advice would be not to have any of the titles limited to Amazon through select if any of the other books are available outside Amazon. It doesn't make sense that you can get all the movies but one at best buy but the only place to get the first movie is Walmart.
If you want to leverage KDP select, either go all in with it with all your books, or put Book One in but don't use the promo until you get the side stories launched. That way you can use the promo at the end of your 90 days and immediately roll out to other markets and not be exclusive. I don't think you will be happy if you start select when you launch the side stories and now have book one stuck for a quarter of a year on Amazon. Think about it, even if you launch book one with select today. It won't be free until April 15.
You need to look at that 90 day window in your Stratergery.
Don't get me wrong, I like select. I think it is one of the most powerful tools a new author can leverage and I would recommend it to anyone starting. However once you get it all down, it doesn't offer anything you can't get elsewhere and the exclusivity clause gets worse and worse.
If you want to leverage KDP select, either go all in with it with all your books, or put Book One in but don't use the promo until you get the side stories launched. That way you can use the promo at the end of your 90 days and immediately roll out to other markets and not be exclusive. I don't think you will be happy if you start select when you launch the side stories and now have book one stuck for a quarter of a year on Amazon. Think about it, even if you launch book one with select today. It won't be free until April 15.
You need to look at that 90 day window in your Stratergery.
Don't get me wrong, I like select. I think it is one of the most powerful tools a new author can leverage and I would recommend it to anyone starting. However once you get it all down, it doesn't offer anything you can't get elsewhere and the exclusivity clause gets worse and worse.