All different search engines will rank your page differently however most of them will weigh heavily on content, keywords and meta tags.
Originally Posted by c.mclean
In answer to your second question
Metatags do not have to be any particular length however usually a good 8-10 word description will do the trick. Meta tags are there to tell the search engine what it is your page is offering for example: The meta tags for 'Template Monster' website use the following metatags
The meta tag should have at least 2 of your keywords, which for the above site "Templates" is one of those keywords, within them but the meta tags are not all that the search engines use to rank your site.
"Template Monster offers professional web templates, flash templates and other web design products available for immediate download.".
The search engines will look at your website title which for 'Template Monster is
As you can see they have again included some of their keywords in the title therefore giving more relevence to your keywords
<title>Web Templates, Flash Templates, Website Templates Design - Template Monster </title>
Your page content should also include your keywords but don't add too many as the search engines will see your site as spamming or a doorway site which is basically a site which is loaded with keywords and when the customer goes to it they are automatically redirected to another site. Also don't add too little as your page will be seen to have no relevence to the keywords and therefore ranked lower.
And your last question:
You don't need to add all phrases however they can help so it's entirely up to you.