Many people write key on notepad and save in disk, but virus can find this files. I think is good idea write key on paper and cover in safe place. Maybe is old method, but if you careful is good.
it depends, would you want people uploading your software for the world to download for free? would you like 1 person to buy and 1000 people to download it off the buyer for free? if not then i would suggest you install activation software. it might be expensive but could save you $$$ in the long run