I don't think there is any scale you go by, but I'm not sure.

Ah scripting, something I just learned how to do this month. This might help you: http://forum.halomaps.org/index.cfm%3Fpage=topic&topicID=34381&start=1
That was me asking how to do simple stuff, like making checkpoints. Nothing advanced like "A tank will spawn and lob nukes everywhere,"

I'm not sure about your graphics, send us a picture of whats wrong with them, then we might have a better idea of whats going on.

I don't know about good voice actors you'd have to ask around, maybe the people making Lumoria would help you(they use voice acting).

That's all I can help you with, hope it helps!