I'm the last person to put down someone for experimenting with bonsai,
but when I started, and asked nearly the same question about oaks,
someone told me they were quite difficult, because of the long taproot
and slow spreading of finer side roots. They take a long time to grow
in pots, and the leaf sizes don't reduce easily. I disregared all these
cautions, tried to grow them anyway and my seedlings witherd in thier
pots for one or another of those reasons (not to mention I was a little
overenthusiastic about my watering as well). I'm not telling you to
stop doing what you're doing, but just ealize that this was a fairly
experienced bonsaiist. I would keep a few easier-to-tend species just
so you don't get discouraged if the oaks don't make it.