Hey ButterflyRN, I've felt the same way about my cats. I do cat rescue actually, fostering kitties until they are adopted, and I just nursed one of my babies through congestive heart failure! He actually came through like a champ but needs medication twice a day, and I've been afraid to go away overnight to visit my girlfriend. Same as you, worried he or another kitty will go through an-xi-e-ty!
That said, some of my kitties have gone through hard times, some have been abandoned by their families (sometimes for good reasons like developing a terrible allergy - sometimes b/c they just discard their animals cuz they're no longer 'convenient'). And cats are extremely adaptable! They do miss their people, but they respond to their environment cuz they're very 'in the moment.' It sounds like you've picked a great place where he'll get attention and be able to move around. Maine coons are very friendly aren't they? He'll be schmoozing up the people at the spa from day one, I promise... And he'll be very happy to see you when you pick him up. The blankets and toys are a good idea.
i love the smell of doughnuts in the morning. it's the smell of... victory!