I know exactly what you mean by it feeling overwhelming! My son was diagnosed when he was one

I have to say I felt very overwhelmed for almost a good year. I think its almost harder on the parents, at least it was for us.
He is now 15 and has been on about 8 Disney cruises and he does absolutely anything and everything anyone else can do.
All the excursions will say -ok, almost all of them- will say it excludes anyone diabetic, but we always do them. There isnt a reason why a diabetic cant except for the fact that they wont be liable should something happen. I always bring with snacks and make sure we have enough insulin. He's been snorkeling, jet skiing, etc no problems, just need to be prepared with snacks for lows and insulin for highs
I agree with having extra supplies along, assuming you are on shots and not a pump just make sure you bring more than enough. When you get to want a pump, you can get travel pumps, at least Medtronic has that program, that they send us a loaner pump for a "just in case" situation so you don't have to bring extra syringes with.
On the first night I always order 2 apples juices for night time to keep in the fridge then when I am testing him at night if he is low it's a quick and easy carb for us.
You will get really good at guessing the carbs..... I mean really good, so that will come but only with time. And also all carbs affect people differently so you and your child will get to know those foods as well.
Hang in there, it will get better!!!
Oh, and after you know about diabetes and know what to look for....you will see people testing and people with insulin pumps on their swimming suits which I would never have even took a second look at but you will notice that around the ship now. You are definitely not alone. Disney will also put a sharps container in your room for the syringes. Airlines don't even bat an eye at insulin supplies....I don't even say anything anymore, just throw our 'diabetes bag' to get x-rayed and they never say a word.