Awesome start sending Google your sitemap straight away - don't forget to update every few months if you are making minor changes to the structure of the site and straight after you do big changes to structure.
SEO questions. @closetnoc is right - stop reading. The internet has too many people saying the wrong thing about everything. There is no difference between www or non www. I would recommend the non-www if you plan to not have any subdomains in the future - its neat and short and its a pain to type the extra three characters when you don't have to.
CNAME issues and server farm questions: All untrue and likely not to effect you at all. I want to strongly stress that you don't need an expensive setup or expensive hosting to have www or non www. Someone is trying to rob you blind with that article.
CNAME is short for Canonical Name record - its a DNS record. It's used for aliasing names - which I highly doubt is reliant to you. It's more for people want to redirect there traffic to a different domain or make it appear as a different domain. Its a very rarely used setting for most web users and if you get to the stage that you are making DNS changed I'd recommend hiring a webmaster because getting it wrong is easy to do, and the results are bad especially if your website is serving lots of customers
NOTE: A subdomain is a domain like webmaster.stackoverflow.com where the top level domain is stackoverflow.com (just in case you needed a refresher)