Can the created New Custom Field for a particular project be imported / copied to a different project?
If yes, will it be possible by batch or just individual custom fields?
Custom fields cannot be copied between projects, you need to create them on each project individually.
On the other hand, when creating a new project, you can request to copy the customizations (custom fields, values, workflow and groups) from any one of your existing projects.
Just remember to let us know about this during your new project requests.