I think one way to get around the side scrolling to add some java script to slowly scroll the portfolio this would then show your visitors that it is a side scrolling page.
On the contact page the form is great I much prefer these from a user and admin point of view. Adding a email address to the page will mean when spam bots finally get round to trolling your site this is email will get added to their database and then the spam begins. On thing I would urge you to add is a contact telephone number, even on a computer support site users had difficulty filing in the form
As for browser support I primarily design sites to work in Chrome and Firefox these days which tends to mean most browsers with the exception of IE will work. But I do generally have 2 style sheets one for IE and one for everyone else and using PHP will set this dependant on the browser being used.
I would recommend adding more keywords to your meta data it never hurts.
As for search bots etc create a robots.txt and sitemap.xml, then get these added to google's trawler.