Congrats on your new bike!

I do want to clarify one point: I don't think a saddle should necessarily be centered on the rails, although it's a decent place to start for a test ride. A saddle may be placed fore or aft on the rails depending on where the riders' knees need to be relative to the pedals. I, for one, usually place may saddle way back because I have long femurs relative to my leg length.