Dave,
Do you have any idea of the kind of game you want to play? I mean here are you looking to do smaller actions where say the player will have a brigade - 5 or so units? Maybe you want to do full historic battles with more or less detail?
For example we play with 3 sets. The first is a home grown set (which will be published next year) for 'brigade' type battles where the Swedes will have 5 or so units of around 20 figures (25mm), the enemies of the Swedes of course have a lot more units. Another set is for full historic battles which we do with 6mm or 10mm figures. We use a set called Twilight of the Sun King: Birth of the Age of Reason which allows full battles to be done 1 player vs 1 player in a single session & with smaller armies. Sometimes we use the Polemos Great Nortern War set which is kind of in the middle of these. You can do full battles but in more detail and with more players/time/resources or intermediate games.
Generally I would avoid general rules sets as the GNW is quite a strange war that is difficult to do with non specific sets.