2) Yes you will be able to install win 7 from dvd that came with your laptop. It will install a clean version.
3) Use the key from windows sticker at the bottom of our laptop. It will activate your laptop.
4) I am not sure about this question but if you format your hardisk you will not be able to create a recovery drive separately like it came by deafult. Also the recovery disk consist of windows 7 with all bloatware like the win 7 came with your laptop.
But before you clean install windows 7 make sure you download all drivers + software(webcam software, fastaccess software + dell quickset so you get the touch buttons at the top of the palmrest + other dell software only if you need them).
First install chipset driver and then all other drivers. Also install Inter graphics driver first and then nvidia driver and intel wireless driver before widi.