Should a commercial web site have www before the domain name to make it look like a more legit business site. Without the www in the URL does it seem like more like a blog?
I personally don't think the www. matters for legitimacy and appearance. But if there's any way you can manage to get a hold of a .com domain for your business, that is much more important. In my opinion.
It doesn't really make a difference in whether a business has a URL with or without the www. The distinction lies in the business's domain name and their customer service to people (customers) who visit their site and interact with them.
Depends on the domain. If you are using the domain name as the brand, then it often makes sense to not use the www. Example: business.com. If you have a more generic or descriptive domain name, I prefer to use www. In either case, make sure that you redirect the www or non-www to the other so that you don't end up with duplicate sites or lost visitors.
What's the best way to redirect. In Google Webmaster Tools i've set the preferred domain but should i be doing something beyond that?
Make sure you do it on the server as well. Use .htaccess to redirect to the domain of your choice. Here's a guide on how to do the redirects in htaccess. Both www to non-www, and non-www to www are covered: http://www.webweaver.nu/html-tips/web-redirection.shtml