If you are optimising for those 5 keywords as a phrase, then I don't see how Google would penalise you.
2-3 keywords in a domain will do, but it depends on the theme of your site. Google favors the use of long tail keywords as a domain name.
CoopersPick, SEOMoz has recently published some research on this. Keywords in the domain are good. But shorter domains are more effective than longer domains.
I have 3 rather long words in my domain name and in hindsight it was probably a bad idea. Oh well, thems the breaks
short URL always do the trick, min. 5 and max. 6 words URL is good and ideal as per SEO requirements. Short URL are easy to remember which make it user friendly.