I was just there yesterday alone with my 6 and 3 yr olds. I think you might be able to do most of your list if you do not do BBB. If you do, there's no way. We did about the same number of attractions and also park hopped, but we did not do anything over a 20 min wait. You have a few on your list that will put you over. Plus, as pharmama said, I don't think they'll let you go on Gadget's Go Coaster or Splash Mountain without another adult.
She can go on both, most likely. Splash they consider it as a everyone is in the same vehicle. So one child could sit next to her and the other directly in front of her. With Gadget's we have been allowed to sit with one child and have one in front. But that may be at CM discretion.
That's good to know. I wasn't allowed to have 2 5yr olds in the same Matterhorn car as me, they had to split up. Luckily, we had an 8 yr old and another adult. It doesn't seem any different than what you described at Gadgets Go Coaster.