Can i transfer data to my new iphone after it is set up completely?

If you want ALL of your old iphone data including text messages, settings, home page layouts etc as in the article you started from, and you have not added new data to the new phone yet, then wiping and starting again is easiest and quickest. Pick your Quick Start method during setup, in fact if your old phone is powered up and next to the new one on tge tabke it will offer you Quick Start phone to phone transfer as first option.

Restoring an iCloud backup is also an option but you still need to wipe it and start again.

No you will have to wipe it and start again

Settings, General, Transfer or reset iphone, erase all content & settings

There are ways to transfer photos, but not where they become part of the "Camera Roll". If they're saved on a computer folder, all images/videos in that folder can be synced with the iPhone. Maybe also sending photos as email/message attachments, although downloads of those photos would be copied over to a different file folder.

iCloud may be the easiest.

you can select photos and share by airdrop or email.

you can sync to your computer and then sync the new phone.