It's the first time two of my players decide to build a magical group and get some initiation. They get the firs level of initiation with an ordeal and they chose to do it with an astral quest.
First question: because they still not have the first grade of initiation: do they have the possibility of going into the metaplanes or do they have to choose another ordeal?
After completing the ordeal (astral quest) they opt for the combination of +1 Magic and +1 Metamagic technique.
Second question: If I understood well, gaining a garde of initiation give you the opportunity of learning a metamagic, but this is not immediate: one need to find the metamagic through astral quests, tutors or free spirits.
They cannot learn the metamagic from a senior initiate or a free spirit: they must do an astral quest. Does this mean that they must do ANOTHER astral quest (other than the one for gaining the level of initiation, for a total of two astral quests)???
Third question: one of the reason why one can do an astral quest is learning metamagic: can one do an astral quest for metamagic even if has not yet gained another initiation level? (I think no, but it is worth asking)

First Question: You have to already have access to the Metaplanes (Initiated Full Magician or via Free Spirit Astral Gateway) to do an Astral Quest as an ordeal. So normally, someone who's initiating for the first time couldn't do an Astral Quest. There are references to Totems opening gateways, allowing shamanic magicians and totem way adepts to project to the Metaplaines for the purpose of an Astral Quest ordeal.

Second Question: You would need a second Astral Quest to learn the Metamagic. If it's your first Metamagic, though, the Quest will be fairly easy. If you aren't a full magician, however, you'll have to find some other way to learn the Metamagic. (Or another way into the Metaplanes, like the Free Spirit power Astral Gateway, or a astral rift or something like that). I don't make it too difficult for my players to find Initiates to teach them the more common Metamagics.

Third Question: Nope. One per Grade. But there are plenty of other uses for Astral Quests that the interprising full magician can exploit.

1) The only ways to get to the metaplanes are to project there, or have a free spirit use the Astral Gateway power. Since you can't do the first until you initiate, they have to do the second or choose a different ordeal (I recommend *not* doing an ordeal for the first initiation, and doing Oath, Thesis or Meditation for the next).
2) Yes, they'd have to do *another* astral quest. You can't use the same astral quest for more than one thing.
3) You can certainly try, but you can't actually learn another metamagic technique unless you gain a new initiate level.