Welcome Doug,
You don't need to brine, it's a preference thing. It alters the proteins and can help give you a more moist end product. This buys you some insurance against overcooking and drying out the bird. It can also change the texture, some people like it some people don't. If you brine it for a very long time in a strong enough solution it becomes very 'hammy'.
You can flavor brine as well. This is adding flavors to the brine instead of just salt sugar and water. Look around the reference topics on this website as well as the recipes section (Poultry Recipes).
As for cooking there is no real benefit to cooking a bird in the BBQ range (225-250). Some cuts of beef and pork DO benefit from the low and slow (brisket and shoulder for example). This isn't to say it's wrong, you can do a turkey in that range if you want to. It will take a long time, can dry the meat out and can remain unpleasantly pink particularly around the joints. Brining is a good idea if you plan on cooking it in this range.
On the WSM I'd suggest you cook it over two fully lit chimneys of charcoal (hot smoke) with or without an empty/full water pan. Water in the pan will reduce your temperature, but you avoid excessive drippings smoke. An empty water pan will smoke like crazy in this configuration as well. I personally don't like too much poultry drippings smoke.
