Convert Static HTML Website to WordPress – Impact on SEO and SERP Ranking

I am converting a static HTML website to WordPress. The site currently appears in the Google SERPS on the first page (for a certain set of four search keywords) as http://www.domain.com. My concern is how the site conversion might affect this.

To minimize the chance of any negative SEO impact, my plan is to copy/paste all <title> tags, <meta name=”keywords”> tags, <meta name=”description”> tags, <h1> tags, file “alt” attributes, and all page text content exactly “as is” to the new site.

As far as page names are concerned, all pages in the existing (pre-conversion) site have .php extensions. The Home page is index.php, and other pages are aboutus.php, contactus.php., etc. For the permalink Structure Tag I plan on using %postname%. I also plan on assigning page “slugs” which are identical to the existing page names (index.php, aboutus.php, etc) instead of using .htaccess 301 page redirects.

I want to make the new (post-conversion) Home page a static page (using Settings > Reading in wp-admin), but WordPress does not allow you to assign a “slug” to your Home page (it assumes http://www.domain.com) – will this be an issue?

If I understand correctly how WordPress works, every time a page request is made, index.php at the site root level runs to do all of the WP initialization, etc, and then the page request is handled accordingly. Might there be a conflict because my Home page will have the same name (index.php)?

Also, I haven’t checked to see what Preferred Domain is set up in Google WebMaster Tools for this site, but I’m thinking that might be a factor in this as well.

Again, my objective is to perform the site conversion so it’s “transparent” to Google in terms of where the site appears in the SERPS.

If you’ve had any experience with site conversions like this, I’d sure appreciate any input you can give me regarding your experience.

Thanks.