The content attributes can all be merged, comma separated, in one robots meta element. I think it's probably best to do that for the sake of not confusing the indexing. Repeating some elements has been known to confuse things.
Google clarified that when nofollow was first introduced in 2005. Sorry I can't find the original reference today for general crawling, but here's one for the Google Search Appliance: [code.google.com...]
