The cube can last several weeks, but that will depend on that product. I typically replace mine when it no longer smells. You can just scrape out the wax or you can also you the wax paper cups they include. I don't find removing the wax an issue.
That is going to depend on the wax cube sizes, but for reference I use the Febreze wax melts and I put in two wax cubes. The cubes I use are about 1 inch x 1.5 inches x .5 inch.
