"I thought about giving bonsai up all together"
GIve up because you lost a White Pine? EVERYONE loses one of those. They are subject to all kinds of fungal problems. They're not easy. At least not as easy as Black Pine or even native pines.
For what it's worth, I managed to kill off a $400 specimen Scots pine. I never thought of giving up, just to find a way to explain the loss to my wife
also, why are you set on Japanese Beech? Native European beech is hardier and cheaper...