You can delete a sample (or a whole book) at the HOME level. Put cursor at the book, toggle LEFT on the toggly-thing, and press down on the toggly thing to verify "Delete". If you delete a book you actually purchased (not a sample), it stays in your amazon account and you can re-download it later, if you like.
M-edge is a brand of cover - search on Amazon. Very nice covers.
www.decalgirl.com has very nice skins (decals) to prevent minor scratches. Mine arrived just yesterday.
I think one enters
www.mobileread.com/mobiguide to download the "book" which is, in fact, a list of what books are available. Then you just click on one of the books, and it automatically downloads straight to your Kindle. You can also download books to your computer, and push them over with a USB cable.