There are no hobby ranks so that part doesn't apply. But I would let a character start developing Directed Spells at the same point they are learning a suitable spell. For a Magician or Illusionist who gets applicable spells at 2nd level, they could start play with those spells and the skill. For a character who won't get those things until a higher level, they might lag a little bit, e.g. Druid gets Shock Bolt as a 4th level spell, in principle they could learn that as a 2nd level character and if they did I would let them start buying ranks in Directed Spells at the same time.
For practice purposes, you can take time to prep, you can yell and use both hands etc, so unless a spell is well above your level you will usually be able to cast it. And many spell failures let you complete the spell too (maybe after an extra round or at extra cost). So I don't think overcasting should prevent learning the associated skills.