they should not meet in session 1.
Strongly disagree. Nothing wrong with doing that, but nothing wrong with having them meet in session 1 too, as long as you have built characters who will be willing to go along with the GM's hooks.
And even that part is flexible, depending on the nature of the hook. If the hook is "you see an ad look for rat exterminators", then you better have a character who wants to be an adventurer and will cooperate with other would-be adventurers. If the hook is "you're prisoners being ordered to go explore this dungeon by order of the vizier", there's room for slightly less cooperative PCs, as long as you PC is cooperative enough to go along with that order, even if (at first) reluctantly.