You don't have a framesize limit. I don't remember if you can import your footage and use that as a reference when creating your particles, but I think you should.

Layering, well there's no layering in PI, so it's better if you render out your particles as separate passes.

All of the stock effects are editable, and you can even replace the sprites in any effect with sprites of your own.
BTW I don't really think you're going to get anything easier than Particle Illusion for the work you're trying to do.

nemirc
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