robots.txt, SEO, meta, other general advice needed

I have my site jrandolphsteele.com running on hostgator using 3.5.1, twenty twelve (+child) theme, akismet and W3 Super Cache plugins, and Google adsense. I now find myself more than a little confused regarding some of the things I should do next and searching for answers has not helped. Mainly because the information that I find is often conflicting and it is difficult to determine what is applicable to my wordpress version and theme versus other versions/themes. I am hopeful that someone on this forum can offer some advice.

1) Does Super Cache and .htaccess negate the need for a robots.txt and, if not, what should robots.txt look like?

Some search results say yes and others say no and others say robots.txt is already there by virtue of installing WP (it is not in my case). Specfically; I have modified content.php to only display excerpts on the home and general category pages. It seems to me that the crawlers should skip the home/category pages and not the individual posts. Yet; I want WP to still be as SEO friendly as it is designed to be.

2) Do I need to, should I, add some meta infomation to the header?

Again; the information I have found is conflicting/confusing. If I were to describe my site it would be something like: Electic commentary, opinions, essays, poetry, and more about anything and everything. When I defined my categories I did add a description for each similar to that. So far as I can determine that only shows up on the category index pages. I would like the search engines to find/list my site under the general categories listed in that site description as well as, or instead of, the more specific categories I defined such as Technology. I can’t figure out how to accomplish that.

3) Should I add a link to favicon.ico to the header and what folder should it really be in?

I placed the favicon.ico in the root site (WP) folder and it shows up fine in my browser as expected. But; I’ve read that it should be linked via the header information. I’ve also read that it should be placed in the Content, or Themes, or specific Theme, or child Theme folder(s). I don’t want to put it everywhere if I should not be doing so.

4) SEO plugin or not?

I’ve considered it, specifically yoast, but again there is conflicting and confusing information. Firstly; WP is supposed to be, I think, already very search engine friendly. It seems like adding a SEO plugin would be overkill. Secondly; it seems that there might be some problems with WP Super Cache and SEO plugins both active. Finally; I can’t figure out if yoast, or another, SEO plugin would help me resolve the first 3 questions/issues or not.

I realize that it is a lot to ask and that this might not be the best forum to ask the questions. I’m new to blogging and WP and somewhat lost at the moment. Any advice, info on best practices, or links to help me find my way would be appreciated.

Thanks!