Hey Cemal,
1. We look at all Apps before we publish them to the App Store. What you've listed here are the permissions that the App is asking you for. This describes what the App can access, and what the App is adding to the admin interface. This is all normal.
2. You should not have to clean anything after you uninstall an App. The App itself may keep information on its servers, but that's at the App developers discretion.
3. An App should not be able to break how Shopify functions, although if you give an App access to edit or add information, then it will be able to change information on your shop.
I hope that answers your questions!