Should I plant the germinated seeds after I have some good size root even if there is no sign of the shoot or should I wait until I have signs of the first shoot/leaf?

We prefer to plant the seedlings as soon as the first sprout appears. If you wait too long the roots get entangled and may be damaged in transplanting. Most palms are tougher than one would assume in their early stages, but no palm likes root disturbance.