I dont believe it to be a monthly fee thing since you will be able to buy it for a 100 bucks like any other windows system but there may be different purchase options like a subscription if you prefer that. Im not really sure what all the options are there. All the other previous windows are going to be unsupported just like xp. You will basically have to upgrade at some point. There really is no reason not to. Windows 10 is so much nicer in almost every way. I have been on the insider program for a year now so i have had it insalled on 3 machines for about that long. The only thing that i dont like is their mail app. I think that is terrible so i use 3rd party. I have never had any issues with any software not running. Keep in mind that the basic core of it is windows 8 and its just a user interface change for the most part so compatibility should be a non issue.