I happen to have a bit of expertise regarding this last point and I thought I would share a few tips for artists and crafters looking to sell their work online.
1.) Be visible.
This may seem obvious, but a strong and varied online presence is important to your success selling online. Don't rely on just one platform to share your work. A website and/or blog is typically the foundation of any online presence. You can use it to tell your story, share your work and even sell. If you choose to sell instead on a site like Etsy or ArtFire, a website or blog is still important to bring customers to your selling page. You should also maintain a diverse presence on social media sites. Consider creating accounts on Facebook, Ravelry, Weavolution, Pinterest, Twitter and/or Instagram. Remember to not start with more than you can handle, though, as you want to keep these accounts active. A social media account can be a very powerful tool, but only if you use it consistently (more on that in tip five!)
Looking for a cheap/easy way to get started with a website? Consider an easy sitebuilding program like Squarespace or Weebly. If you're looking for something free, Wordpress and Blogger both have free blog or site options.