HI Melissa5844, thank you for posting in Apple Support Communities.
If you have saved your photos in iCloud, with the AppleID you are wanting to use, then they will be available from iCloud Photos on all your devices including your iPad.
If you delete photos (saved in iCloud) from the iPad they will be deleted from iCloud Photos on all your devices.
Please look at the following link which explains how to setup and use iCloud Photos:
https://support.apple.com/en-au/HT204264
In regards to storage, the link above also explains your storage consideration requirements as follows:
Make sure you have enough storage space
The photos and videos that you keep in iCloud Photos use your iCloud storage and your device storage. As long as you have enough space in iCloud and on your device, you can store as many photos and videos as you like. Learn more about iCloud storage and device storage.
Whilst the 256GB will be suffice, if you take lots of photos, you may need to eventually consider downloading and saving your photos to an external drive and the above link also includes information about this, or, if you continue to use iCloud, you may need to consider increasing the storage space of your iPad noting that only the iPad Pro has a higher capacity storage.