Without a lot of post-production work, it'd be pretty hard for you to show a "convincing" army in a film with "only" 10 minifigs. I say "only" because it depends on what you are trying to show. You wouldn't be able to show something like out of one of the Lord of the Rings movies - but why would you want to?
You have plenty of soldiers to show a convincing battle. After all, in most stage plays they show an "army" as being two or three people. They represent the rest of the army.
From what I can see in the photos, were you might fall down is having an opposing army and scenery. But as Sean said, careful placement of the camera can hide a lot of things.
Now all you need is an interesting story. If this is your first film, I suggest going for something short and simple first. A one minute complete film is much better than an unfinished twenty minute epic.
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