Should I repot Japanese Maple seedlings now?

I have three Japanese Maple seedlings ranging from about 4" to 8". They are doing very well ... nice and leafy. When I first got them, they were like little twigs and I planted them in a large plastic bowl with drainage. At its deepest point, the bowl is probably 6". Now that they've grown so well, should I repot them or wait until next spring? I know they need to winter outdoors (I live in zone 5). Would it be better for them to be all together for the winter or in separate pots? Right now, they are all on one side of the bowl because I had planted a bunch of little Japanese Maple twigs, but these are the only three that took. If I don't repot them, should I spread them out in the bowl to give them each more room? Thanks so much! I just love these little seedlings and I don't want anything bad to happen to them!