If not, setting redirect www to non www or vice-versa will create duplicity of site. Because google thinks the www and non-www version as different pages.
Search engine optimization is a process to improve their site with both users and search engines in order to increase the website traffic receives from Organic search.
You can place the same google adsense code multiple times on a web page. The reason goes for different ad code is size. To place google ads which size is suitable for the page you want to track and position in your page to get maximum clicks.
