I don't think there's anything stopping you from selling it so long as you don't run afoul of the OGL and/or any copyrights for anything you use that isn't covered by the OGL. But don't quote me on that.
As for if it's worth it, just look at the number of APs that are already out. People must be buying them if they're being produced on a regular basis. Just look at the list of Pathfinder-compatible products that are available and you'll see that there must be a market for these things. I wouldn't recommend putting out physical books, at least not until you've got a customer base that you know wants them, but if you do a PDF and it's nicely done I figure you'd get at least a handful of buyers. And then you can go from there on if you feel the money made is worth the time you spent.
And for where you'd be able to sell it, I figure you could get in contact with Paizo and see what it takes to be a part of their webstore. And there's DriveThruRPG as well. There's plenty of open/indie ebook markets that you could probably find a place in as well.
I'd say that if you want to do it, give it your best and hope for the best. But don't expect to make an immediate fortune either. Just like every other business venture.
