Only do 301 if the other sites have great value, you say that you have merged all content on 1 site an rewritten it? Google will automatic see the new content, the only reason i think you should do a 301 is if the other sites have a PR higher than 3 or 4, pr 2 and 1 are EASY to get. So take the new uniq content your wrote, combine each site with your different keywords. More on same page are good for results. You dont need a landing page for each keyword.
I would do this:
Check the PR and Alexa for all the sites, figure out if the traffic is real customers or just scans. There is no point in redirecting scan bots to new site, they will come automatic.
Then i would do the 301 from Google Webmaster Tools and make sure that they all go to front site of brand.com site. But only if they have anything to offer for your new site.