We did a 10 day Florida trip at the end of September/beginning of October this year… spent the entire time at Disney and still didn’t get to do everything I wanted! But I have a chronic illness so we had to take it easier than most. The weather is ideal around that time (the humidity is easing off and the temperature goes below 30 degrees Celsius).
This was my 4th trip to Florida, and we’ve done a lot over those trips: the Universal parks, Seaworld, Florida Keys beachfront hotel, mall tours, Everglades airboat tour. Honestly all of it is brilliant, I’m sure you’ll have an amazing time regardless of what you do. We’ve visited Disney as a part of our trip every time though, because I don’t think you can beat it.
If you do go to Magic Kingdom during your visit, make sure to check it’s not on a day when Mickey’s Not So Scary Halloween Party is on - the Magic Kingdom closes to regular guests (aka those who haven’t bought separate party tickets) at 6pm on party days, so you wouldn’t get to see the evening fireworks, which are amazing. Or if you didn’t want to do a full day at Disney, an evening at MNSSHP could actually be a good choice for you - there is free trick or treating as part of the ticket price, special shows/parades, and generally shorter queues for the rides!
Otherwise Magic Kingdom is mostly family-friendly nostalgia type rides rather than adrenaline thrills (though TRON is brilliant), and general experiences like parades etc.
You can also find projected park crowd calendars for the different theme parks with a bit of Googling, and suggested days to avoid specific parks, which might help you decide what to do when. It’s also worth checking the American public and school holiday dates, as crowds can surge massively around those. I planned our whole trip in detail myself, so if you want to PM me at all about anything, feel free ☺️