ok for starters: if i scan socialhero.com with my tools I only get 4 pages returned. With the index being duplicated even. So something is going wrong here.
The 404 error is probably induced by a page linking to a non existing page and returning server code 404. You should follow the links on the site untill you find the problem. Or you can use a sitemap tool that also tells you where are the links are going to and coming from.
The 302 redirects do present a problem. There are 2 different way's of redirecting information. 301 is a permanent version and that one also passes linkjuice, authority and all other things. 302 has been reseached and tested by some of the biggest names in the SEO world and passes on almost no linkjuice/authority. Use a .htaccess file to redirect the pages to the correct location.
The 92 missing meta description tags I would also solve as quickly as possible. Although there is no direct correlation between higher rankings and meta-description tags there is an indirect correlation between the two. As you may know Meta Description tags are used by the seach engines to show up in SERPS and telling the searcher some information about your page/site. Using this information correctly you can influence the searcher a bit by making your description look enticing of irresistible. By doing so your CTR (Click through Rate) will go up and Google measures CTR. Higher CTR in combination with more time spend on the page equals to a great page. Why else would the searcher click on it and stay on the site?
Those factors are known to be used by Google to determine rankings. So that is the indirect link between descriptions and higher rankings.
96 notices about rel=canonical all depends on how they are used. If there is only one canonical tag in the entire site (for instance every page tells the search engine that your homepage is the original one, you're in trouble). So check that one out to but I wouldn't spend to much time on it.
As for some learning material:
MOZ.com beginners guide to SEO is a great way to start. If you manage everything in there you can move along.
http://moz.com/beginners-guide-to-seo
another great resource are the Youmoz and Moz blog on this site. I spend more then 1000 hours on there resources alone to learn more about the subject. So if you really want to be a great SEO/Inbound Marketeer/Web Marketeer be prepared to do the same.
Hope this helps you out some.
oh yes the book by Danny Dover is also very usefull:
http://www.dannydover.com/lp/seo-secrets.html
regards
Jarno