Honestly, I would go with your husband to his doctor appointments, general, cardiologist and surgeon, to see what their opinions are about the trip, heat, roller coasters.
My Dad had a quintuple bypass about 6 years ago. He never had a heart attack prior to that however, so that does change things in this scenario. His cardiologist, prior to surgery told him he could do what he felt up to doing, but if he had any chest pain to rest, try his nitro and if he continued to have problems to go directly to ER.
One of the first things that your post made me think of is flying. His cardiologist didn't want him to fly. So, ask questions, call if he doesn't have scheduled appointments. At the end of the day though, he is an adult. You can certainly give him your opinion and discuss how you are feeling and your worries about the future. Hopefully you will be able to reach a decision together, I'll be keeping you in my prayers during this hard time.