First thing to do is to rewrite your form_valid method in SignUpView to account for the information provided to you at base64 user ID object error for email activation - #8 by KenWhitesell
This includes eliminating the roughly 20 useless queries that you have written in it. (Almost every instance you have of CustomUser.objects.filter(...) is unnecessary.) Issue one query to retrieve the object, then use it as needed throughout the view.
Also, it will be helpful if you posted your CustomUser model as that appears to play a key part in this, along with your CustomUserCreationForm.