Linking and inserting Facebook friends in Database

I'm developing an application that will need to know the friend's connection between registered users in my system.

So, importing those friends are one step of the process. However, I want to do it in the best way possible using MongoDB to reduce CPU and Query time.

I have basically 2 questions:

1) Should I keep the friendList record of each user inside it's own model (User), or with reference, in a new model (FacebookFriendship)?

// Nested (User Model)
{
    [...],
    facebookId: 12345,
    facebookFriends: [123456, 12313, 1241],
}

// Reference (FacebookFriendship Model)
{
    friendA: 12345,
    friendB: 12344,
    // Or maybe an array?
    friendship: [12345, 12344]
}

2) Other than the Model structure (That gives me a headache), I'm trying to figure out the proper way of importing things to the server.

Since I only need to know the friendship of those users that are already registered, I don't want to import all the friends of that facebook User.

In resume, what I want is to import those friendships, only if A and B side are both registered (The new user, and it's friend).

What I thought is something like this:

foreach Friend of newUser as friend:
   if FacebookUserExistsInServer(friend):
       createFriendShip(friend, newUser);

However, this approach requires a LOT of queries. Let's say 500 friends: 500 * 2 = 1000 queries for just one 'new' user. And I would still need to 'refresh' that data latter.

Is my approach a little too intensive, or ok for a normal application?

Thanks anyway!