Actually, using social media and article writing WILL help your off-page SEO because you will be receiving high quality backlinks to your website. Just be sure not to "stuff" your main keywords in the content you create on these sites.
yes and you can also learn SEO as you go. I recommend browsing amazon for seo basic training ebooks, pay attention to the reviews make sure they are real people giving the high reviews not fake bots.
everything you do while marketing or advertising online should be done with your SEO purposes in mind. You just need to do some research and find out which keywords you want to use. pick 3 keywords that your perfect customers will be looking for and use them. cheers jason