1) That sure depends on the type of your game - for an RPG, I'd say this is sure all in the green. For an RTS or something, this'd be far too high.

2) In racing games, where the cars are about the only "real" models you will see, you can go with around 10k polies for each IMHO. In other games, I'd rather set myself a limit to around 3k to 5k polygons...

I know this is all rather vague. I guess you'll have to provide more information on your project to get more precise answers.