I really like the Banfield Wellness plan but it depends on the vets that are working there. I have found it a great value and it includes six month preventive care appointments. This allowed us to catch our old girl's lymphoma at a very early stage and enjoy 16 months with her. Plus, I have never had to wait for an appt. if I have any concerns.
As for age of spaying and gastropexy, I'll leave that to more experienced folk.