1. yes you can do that, the parameter for include can be a string, btw, $PAGE is not equal to $page
2. nope, can be any extension, usually people use inc
3. its totally up to u, ppl use full name as its easier to debug, ppl use abbreviation because they dont wan the end user to know what is passed in the url
4. yes, its can be anything, just make sure you $_GET['act'] the correct variable