Deleting iCloud photos

Nope. iCloud Photos is a syncing service to exactly match the photos on your device to those in iCloud when you use iCloud Photos. You would need to shut off iCloud Photos on your device to store them on your iPad only. With iCloud Photos turned on, deleting them from iCloud will also delete them from your iPad. If you do not use iCloud Photos, you can delete them from iCloud and they will not be deleted from that device, but will be deleted from any other device that is using iCloud Photos.

No problem. If you do choose to turn off iCloud Photos, make sure they have all been downloaded to your iPad before you delete them from iCloud. You should be able to see the progress of the downloads at the bottom of the screen in the Photos app. Also if you turn it off, make sure to choose the option to keep the photos on your device.

When not using iCloud Photos, the photos will be backed up to iCloud in the backup file when using the iCloud Backup, so you will see the size of your iCloud backup increase. You can choose what data you want to include in your backup file. To avoid data loss, you should use either iCloud Photos, iCloud Backup, or manually store your photos in another location.