When I said spinning around, I meant, holding him in your arms and spinning as if you're dancing with him. Not spinning the baby like a top.

If he's never been on slides or any kind of rides, you might want to try it out before your trip just to get a feel for things. My kids both loved going on slides even before they walked, although I totally understand if you're not comfortable with that. They'd also been on rides at fairs and parks so I had a good idea of what to expect before Disney.
My best advice for Disney with a toddler is to manage your expectations before the trip and don't over-plan. This will be an amazing trip for you because you'll get to show your baby a magical world. But he might not get all of the magic yet. Doesn't mean he won't have an amazing time. If he doesn't like the dark rides, no big deal - there's plenty more to do. Personally, I would hesitate to even go so far as to plan a first ride, just because you don't know what you'll encounter when you get to the park and I really think the key to enjoyment with a toddler is going with the flow. Most of the dark rides have some element of fear at some point, so if you're looking for a sure-hit, maybe skip those at first. But if you're looking for a safe, no-risk first ride I agree with the Casey Jr train or King Arthur's carousel, maybe even Astro Orbiters. If you're looking for something more iconically Disney, maybe It's a Small World?
You'll have an amazing time and make great memories. Enjoy your trip!