In reply to Shack.

Good planning and especially having the passion for WordPress.As for Underscores, technically it's not a framework, but more of a starter theme that you modify and use as a foundation...which I use myself. It's a good starting point though.

As for WordPress standards, it's best to get that from the Codex because you are getting it right from the source. Using the underscores is also a jump on standards. I kind of wish I had my blog tutorials up and running on my site because this is what I plan on doing with my new site Shaped Pixels (technically my 3rd site), but for other sites, wpbeginner is a possibility, but I would say start here: http://codex.wordpress.org/WordPress_Lessons

Regarding Theme Forest, it sounds like you want to try that out on the side, so that is a smart decision and to give it time to see how things go. I'd also consider reviewing their licenses thoroughly, but please note that if you plan to have your themes on the WordPress site theme directory, your themes will need to be 100% GPL.