I'd suggest even just 40-50 in one bracket. Levelling is pretty fast and that way the 40s can get some early practice in, and the queues won't be too bad. Even a fully twinked 39 isn't that OP against a lv 25, and people level so fast that 10s are going to be rare anyway. Just one bracket split, pretty please
OTOH if no brackets and regular release of new content then newbies will get progressively more insanely roflstomped mostly based on gear and stats alone. Funmuch?