Also, we can do a lot of character differentiation with costumes and character design. PJ's dwarves in the Hobbit are an obvious example (every one must have a different hairdo!), but another example is the Skeksis and the Mystics in the Dark Crystal. Almost all of them are background characters (and in the case of the Mystics, do not have lines). They do all have distinct characteristics, though, so it's not a mass of identical aliens. Certainly early on, all we are going to know about some Valar and Maiar is....what they look like. Until they are part of a scene that highlights them, they won't come to the foreground and make an impression on the audience.
Nessa would likely be 'random dancing girl' until we get to Episode 5. But she can certainly appear on screen prior to her introduction. She could be dancing in the rain in a scene where we introduce rain (or snow). She could be dancing alone in a scene where other people are pairing up. Whatever.
Generic group scenes can highlight characteristics we want to bring out. Here is the (disgusting!) feast scene that shows off the Skeksis:
The beginning of this scene can be summed up as: Watch ugly puppets eat! I don't think it's meant to be taken too seriously, but it is meant to show some of the variety within the group. Some are just concerned with the meal; others are talking politics. Which leads into the actual plot-relevant second half of the scene. They aren't *all* exactly like the leader, and this is one of the few scenes where we hear input from the glutton and the epicure.
I am not suggesting we introduce the Valar in a similar way, but if we have an important council (like the end of episode 2, where Manwë is acclaimed as leader), we can see some of the minor characters being themselves, even if they don't really have much part to play in the rest of the episode. Even if the focus isn't on them, they are there and participating and not all cookie-cutters.
In general, I am a fan of using party scenes to introduce people to an entire culture or group.
The Podlings in 'The Dark Crystal:'
From the same film, a true party scene, and one meant to introduce a culture of people who have not really been seen yet in the film. Our main characters keep center stage, and none of the incidental characters are going to reappear in any meaningful way. We're just learning how they live, not who they are.
The dwarfs (sic
) in 'Snow White and the Seven Dwarfs' (Yeah, I know Tolkien was not a fan!)
This one is meant more to showcase the entire cast. Each dwarf has some personality and the viewer is given some insight into who they are. Sure, our main characters among the dwarfs are going to be Grumpy, Doc and Dopey, but we at least see the others in action here. Even the woodland creatures have a consistent background presence. And the viewer would get the distinct impression that the dwarfs are German after watching this, so something of their culture comes through, even if it is just a silly song.
An Irish Party in 3rd class in 'Titanic'
This scene is used as character development for the main characters (Rose is a tough working class girl when she needs to be! umm, yeah, sure, whatever), and the interactions with the background characters are to highlight this. Some of the characters in this scene will reappear later in the film during the sinking of the ship, but if the viewer doesn't remember them, it won't be a big deal. The main point, of course, is to emphasize the class differences between Jack and Rose and show that they come from different worlds. We've seen him muddle through hers; now it's her turn to be clueless in his.
Etc.
All three of these scenes involve introducing a stranger to the group during the party (Jen, Snow White, and Rose), so there is an outsider observing, sharing the novelty with the audience. For the Valar, the newcomer is Melkor (or Tulkas) I guess, so something could be done with that as they would be the main characters during the lamp lighting and wedding, respectively. These would be our first real parties. Prior to that, we can have group scenes, but not proper revelry. Still, I'm not sure that either of them would be 'out of place' enough to fill that role, as we won't have much time to establish how the Valar do things before they get there. But, ah well....
There are plenty of ways to quickly introduce the audience to a whole group of people without naming any of them. But in general...parties, yes
. They are quick and fun and not people standing around talking on screen. There is music and merriment and possibly shenanigans. They can be done in such a way that they advance the plot, rather than bringing the actual action to a screeching halt.