I'm a graphic designer who has designed websites using xhtml and css.
I'm not sure if there's a way to create a SilverStripe Site without touching some PHP files :). The PHP coding can be very trivial though (eg. defining some array entries that will then be used to create the Database fields). Maybe you should check out the Tutorials:
If you can complete/understand these, you should be able to create your own sites with SilverStripe.
As for the maintaining and updating of the Site: I think that's a huge advantage of SilverStripe compared to other CMSes. It's really simple to use.
Just try it. You'll discover soon enough if it fits your needs.