How do I get additional i cloud space for my photos on my iPad

You can look at your iCloud usage in Settings/Your AppleID Name/iCloud, and toggle off some hogs that you don't need . You can also buy more storage. I now have Apple One because between photos, videos, our own music library, and backups for all of our family devices, we need the extra space. Plus I had separate subscriptions for Fitness+, and it wound up working out well for us.

Also when you buy extra iCloud space, you are an iCloud+ member, so you have access to awesome features like hide my email which I adore.

I feel that iCloud is a very poor space to store important photos or data. It is primarily a synching service which means that if you accidentally delete a photo from one device, it will be deleted from all devices and iCloud. It is much safer to save important photos and data to your computer or an external drive.

You may wish to start with this link:

Upgrade to iCloud+ - Apple Support

I agree. An external hard drive is a much safer place to store files and it is under your control rather than some nameless online server which can malfunction or be hacked into.