As far as the rifled barrel get one with the cantilever mount, this way you can take the barrel off and scope will still hold zero and replace it with your smooth bore barrel to be used for small game, skeet, etc.

Don't get into the hype about scopes made just for shotguns, this is just BS from the scope companies. A standard rifle scope will work just fine.

next question, what is your price range for a scope? For me I have Leupold VX-II 3-9x40 on all my slug shotguns. I just placed an order for a new one for $253, this will go on my Savage 220F this fall

Also you can get a Mossberg 500 combo: rifle/cantilever barrel, and a smoothbore barrel with 2 or 3 extra chokes for under $300, The Mossberg 500 is damn good shotgun