28 gauge guns are fine, but I think a 20 is more versatile, because it can hold a wider range of payloads.
People may tell you how one gun isn't ideal for all the purposes you mentioned, but you say you'd like a multi-purpose gun, so I'll go with that.
These might be a tad over your $1000 limit, but Beretta 686/687's and Browning Citoris are often considered the starting point of really well-made O/Us. I've seen some around here for maybe $1,300 used, but I'm not really looking for them, so I suspect better deals are out there.
Also, the Japanese company that makes Citoris (Miruko) has some other O/Us out there under the Charles Daly or Miruko B.C name. I've heard good things about them, and they are less expensive than models with the Browning label. I've seen used ones for $700-800.