Should I buy numerous keyword rich domains?

Unfortunately, there’s no good use for multiple domains when it comes to the search engines. If you try to gain an unfair advantage in the engines by blanketing them with lots of different sites, you will then be into that “deceptive” territory.

Your best bet is to simply park them all at one domain, and then forward the whole lot via a permanent 301-redirect to your main site.

The only other viable option for the domains would be to truly build completely different sites at some of the domains. There’s nothing wrong with having a few sites, but they really should each provide different info in order for them to be effective. Just remember that keeping and maintaining many sites is a lot more work than just having one site that is the best it can be!