Hi,
We have booked for October 16 but now my wife is getting cold feet for the following reasons. Can anybody who has visited with a similar age child help us please.
the child will be too young and won't enjoy any of it.
Absolutely untrue! DS at 11 months and 23 months had fabulous trips. He enjoyed new things each time. And actually, he made our trip more enjoyable by noticing different things that we previously might not have taken the time to see.
Meals will be stressful as the child won't sit still
All depends on what you plan and expect. All the counter service meals will be a piece of cake, as it's open seating, and one of you can walk around with your child if needed. Plus depending on where you sit, you might have an entire alcove to yourselves. For sit down meals, just plan the right ones. Buffets would work well. Biergarten, for example, has live entertainment, and it's expected that kids will run around the stage area during the show.
Queues will be impossible as won't wait up to 30 minutes to go on things.
Again, plan smart and you'll be fine. Wait times are posted, so don't get in line of it says 30 minute wait. (Although some queues are worth it, as there's lots to play with along the way.) Get FP+ for the longest lines, and then ride other stuff that has lower wait times. Also pick the right park to visit each day - check a crowd calendar like easywdw.com
They won't sleep in buggy at night time when we stay out for meals/rides/fireworks
Plan an earlier shift. Go at rope drop, and then plan to be back at the room by bedtime. If you really want to see night stuff, take turns who stays out each night. Depending on what resort you stay at, you might be able to see some fireworks from your resort while child sleeps.
It will be too hot and won't be able to keep him cool
October is not furnace hot like July/August. Again, it all depends what you're used to and what your expectations are.
Will be dificult to find food for him as salt levels will be too high in our food
Check out menus on Allears. Figure out what type of food is acceptable to you. You don't have to get fries- you can ask for apples instead. And you don't have to go to the cheeseburger serving restaurants at all. Good healthy food at places like Columbia Harbour House, Sunshine Seasons, and many other places.
Flight is too long from UK and will be a nightmare
Can't help you there...
He will always wonder off and not want to do or go where we are going.
Not knowing your child, I can't say much here. But I can share that I thought I would need a harness when DS was 23 months, but he wanted nothing to do with it, and it turned out that he didn't run off anyway. We would tell him about whatever exciting thing we were going to do next, and he was in board almost every time. Also figured out that trip that he loved fountains and boats, so we often could get him to go where we needed by telling him we were going to see a fountain or boat on the way. 
Won't sit and wait plus watch fantasia, fireworks, parades, shows etc
Disney is pretty captivating - you might be surprised. DS at 11 months sat through Nemo (40 minutes), and he had never done anything like that before. But also, there are easy exits from everything if you need it. And many things have wiggle room. For example, Monsters Inc DS was able to climb up and down bench where we were sitting, and play with the lamp on the counter.
Sorry know there is a lot of points.
Thanks
Ross