once i create an apple id is my original gmail linked automatically if its used as my apple id?

Creating an Apple ID using your Gmail address as your ID doesn't create any link between your Google account and Apple account (other than it does let Apple know where they can contact you by email).

If your photos are in Google Photos, you may want to install the Google Photos app on your iPhone. You can install it by using the App Store on your iPhone. More information about the app: Google Photos on the App Store

The following has instructions on how to set up Gmail in the built in Apple Mail app: Add an email account to your iPhone, iPad, or iPod touch - Apple Support

Another option (that I use) is to use the Gmail instead of the built in Mail app. It is also available on the App Store. Gmail - Email by Google on the App Store