The APB is OK where it is so long as you get the latest firmware and only run digital.
If you run analog, you'll still want it at the end of a straight, right before a turn, so that the cars' guides are nice and deep for reliable sensing.
I don't see any other issues with the layout, except *maybe* the classic crossover in the pits. It's a great thing, but since classic has a shallow slight, you might be filing down a lot of guides so that they don't catch in those slots. If that becomes a problem, you could also cut the slot bottoms out of that piece, and glue some card stock under it to pad it up and hold the pieces together.
Too many R1? Heck no!