A4 should work for the pamphlet, it was designed with American 8.5×11 in mind but that's the closest size. The size of the journal is based on how you plan to pass it from player to player, as a large one would make it hard to mail. A5 sounds great to me!
Would you consider producing an A4 version of the pamphlet? The aspect ratio of 8.5×11 is slightly different, and I'd love to be able to print it without a margin so that I can fold it without taking scissors to the printout.
