.410 is a little small for whitetails, and they are illegal to use for such in my state at least. A mossberg with two barrels- one smoothbore for waterfowl and one rifled barrel for slugs would probably be the best bet if you are on aq tight budget.

The .410 with some #71/2 shot would be good for squirrels- well actually good for you to shoot squirrels with and bad for the squirrels themselves
If you have the time, spend several mornings squirrel hunting, it will give you a feel for the woods, and what the woods normally sound like, and time spent squirrel hunting will help you out when deer season comes along- you need the same set of skills- walking quietly, sitting patiently, watching for movement, listening to sounds, and most of all sitting really still.