I think you are over thinking things a bit.
There really is no difference in adding Power CMS to an existing site versus a new site.
To try to avoid confusion I Will refer to the Dreamweaver Template as the "DW Tempalte", nd the Power CMS Tempalte as the "CMS Template" going forward
you don't add CMS Content to the DW Template. only to the pages that are based on a the DW template
the use of the CMS Template allows you to create one page in the site, that will change the content displayed on it by use of a URL variable. The CMS Template concept allows you to create one physical page on the site that acts as multiple pages. This gives the user the ability to "create a new page" by creating a new page from the template. So for example:
In the CMS Admin, you create a new Content named "Blog" and you mark that to be used as a template.
In the "Blog" Content, you create 2 Content Areas, "Content" and "Title".
Now in DW Create a new page, for examples sake, we can call it blog.php. you can apply the DW Tempalte to this page if you like. In an editable region add the developer Notes code for the Blog Title and Blog Content content areas where you would like them to display.
So at this point, the CMS Template content is configured and the physical page that will show the content is configured. if you browse to this page in a browser, you will see the content that you entered for the Title and Content areas.
Now in the CMS Admin, Hover over the blog template, and click the green plus button to create a new page from the template. Give this a name such as "one" For this new template page, there will be a set of the same content areas, "Content" and "Tiltle". if you look at the developer notes for this new Template page, there will be a section to display it using a URL variable "?blog=1"
the idea being that if you browse to the page as:
you see the original content for the Title and Content areas.
if you then browse to the page as:
you will see the new content for the template page you named One. the user can continue to "create new pages" based on this CMS Template in the CMS Admin, and you can see those new pages by using the corresponding URL variable.
Now you don't need to use a CMS Template for every page. lets say you want the home page to have editable content on it. in the CMS Admin, create a new Content named home, for this one we won't check the option to use it as a template. Create the desired content areas, then add the developer notes code to the index.php page.
as for SEO content, for your content pages, create the following content areas:
the in your page, add the CMS to the meta tags, for example:
<meta name="keywords" content="<?php echo WA_getCMSContent($database_PowerCMSConnection, $PowerCMSConnection, 'content name', 'meta-keywords'); ?>">
<meta name="description" content="<?php echo WA_getCMSContent($database_PowerCMSConnection, $PowerCMSConnection, 'content name', 'meta-description'); ?>">
<title><?php echo WA_getCMSContent($database_PowerCMSConnection, $PowerCMSConnection, 'content name', 'meta-title'); ?></title>