I've taken all three of my kids to WDW between 9-11 months old for their first trip. We actually are going again at the end of this month and my youngest will be 14 months (this will be his second trip- He was 9 mo on the first).
A trip with a kid that young is not about the kid so if you want to go, I would go. Yes, you can tell a toddler enjoys seeing all the sites and taking it all in, but they would do that anywhere you took them at that age really. When we only had one child, we took her to WDW at 10 mo because we wanted to go to WDW for our vacation that year. To me, taking a child that age is way easier than taking them when they can walk and talk. At that age, they tend to go with the flow
As far as naps, all of my kids napped in the stroller at WDW. We have a City Mini, which is fairly comfortable stroller and they all napped there. We also bring a stroller fan during the hot months. When we only had on kid, her nap is when we used our riderswitches (although that is changing) or shopped. We found it harder to take them back to the resort to nap. They would always just fall asleep on the way back and refuse to nap when we actually got there.
My oldest hated fireworks until she was about 3. We found this out during Wishes at Disney. When it was just her, we did skip the night shows because of that. Once her sister and brother came along and were fine with fireworks, we would do the nightshows even with a baby. We don't tend to do every night show every trip, but we also don't adhere to a strict schedule while on vacation either. If we are feeling up to doing a night show, we do it. If it seems like everyone is cranky and needs to sleep, we do that.
Since you are flying, I would consider using a grocery deliver service such as Garden Grocer or Amazon Prime to deliver diapers, wipes, baby food, etc. I always do this so I don't have to bring all that stuff with me. Super convenient.
At that age, my kids all loved Small World, the Nemo Ride, the parades- really anything with colors. My two youngest LOVED characters at that age. My oldest Hated them at that age. That varies child to child.
Don't forget the baby care centers. They are great for changing the baby and just getting away for a few minutes. Many of the bathrooms only have one changing table. The baby care centers have a number of changing tables. I wouldn't go out of my way to go to a baby care center, but if you are nearby and the baby could use a change, I would use them. They also offer baby items for sale if you forget something. The Animal Kingdom one is especially nice. There is a place for the baby to cruise around the room if he/she isn't walking yet.
I have never flown alone with any of my kids so I can't help you there. Now that I am a mom of three, I wouldn't hesitate to fly alone with my children, but I am not sure I would have felt that way as a fairly new mom. I always pack some fun toys, snacks, and electronics for the kids during the flight. My advice would be to pack as light as you can, but have the necessities for the flight.
Yes, it will be work, but you would have to do most of that work at home anyway. The biggest issue is to make sure you have all the items you will need that you would have at home. If you are staying on property, they will bring you a pack n play. I would definitely get that to provide you with a place to put the baby in the room. I'm sure you mom and sister will help once you are there. I'm sure they would love to see you and the baby.