The new Disney FastPass+

[YepBrook]

HELP!

I posted this on FB, but I thought I would ask here too. I'm so lost with this new FastPass+ thing... trying to set it up right now for our visit at the end of the month.

I am having trouble figuring out how this will work. I'm stuck at step1: Do I make the same selections for all of us even though Grace (5) is probably too young to do some of the rollercoasters we ride? If I give her a separate itinerary does that mean some of our fastpasses might overlap?

I'm also wondering if this means I have to know which park we will be visiting on each day. Lastly, are there certain rides that have such long lines that we will NEED to grab a fastpass for them now that they have this system? Like... get a FP+ for toystory mania no matter what? Can I change my scheduled FastPasses at a later time? Ugh! Help!