You should reshape your numerical layers so that they have a shape (None,4,4,1). To concatenate, you need the all but one axis to be equal.
If you use:
this should work.
Making predictions for new users is often called the cold start problem.
This problem is difficult to over come in a purely item-to-item recommendation system. The most common solution is to include more than just item interaction information. Examples include user profile information and item content information.