1) Absolutely not
There's nothing wrong with having a .html or .php page. Just to clear a few things up, actually. The website would still be in XHTML, nobody could tell differently. PHP, however, would be in the background to generate some of that XHTML (via the include(); statement) - there's nothing wrong with this.
Heck, who knows. In today's dynamic web, maybe the search engines would prefer the use of PHP, Perl (etc). Although one thing's for certain - it's not frowned upon.
2) Nope - unless you are passing a lot of data through a URL. For example "index.php?page=contact§ion=example". Although that doesn't seem to be the case, so ignore that observation
3) How do you mean? Why would you need a meta redirect to index.php? Just have index.php as the only index.ext file, and people will automatically be served with the index.php page. What I mean by that is that if you have index.html, delete it and just have index.php - that way, people will go to index.php anyway.
Using a <meta> redirect would be a very bad thing to do - it'd block out the search engine bots (as they'd come to a page, and get redirected; not good).
Thanks,
Tristan
P.S. PM me if you have any further questions - I may not actively check this thread (I have too many bookmarks at the moment
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