There should be a billion threads on this, but tl;dr: 19" wheels will allow for more sidewall on tires which is cheaper, gives a smoother ride, and provides better rim protection against pothole damage due to the taller sidewall. You can either get performance winter tires which will perform better when it's cold and the roads are clear, or standard winter tires which trade some of the dry-pavement handling for snow/ice performance. A number of forum members (including me) choose the latter. Michelin X-Ice are well-reviewed and affordable. Your local Discount/Belle Tire will probably have them in stock, and you can compare pricing with The Tire Rack.com.
Do some forum searches on "winter tires" and you should have plenty of reading material.
