If you want to hunt deer get the 20 ga heavy barrel with the scope mount. You can also get a steel bar for the stock that will add weight and help soak up recoil (not to fun to carry though

). Basically you would have a H&R ultra slugger.
If you wanted to shoot smooth bore with rifled slugs get a barrel with interchangable choke tubes and some sort of adjustable sights. This way you could put an extra full tube in it for turkeys, a modified for small game and an I/C choke for shooting slugs (modified works to sometimes). This would not be as accurate as the 20 ga rifled bull barrel, but if your shots will be 60 or so yards and in you should probably be ok with the smooth bore and rifled slugs. Especially if the barrel has sights on it you can adjust for the slugs.
You don't need a 3 1/2 for turkeys, 3 inch mag turkey shells will be plenty and kick like the dickens.
Paul