1. you can screw it wherever you want. unlike mechanical disks it doesn't need perfect stillness.
2. preferably with the details text below. but it will work either side up. it's not affected by how it's placed.
3. depends on your exact config. but typically windows 7+ will have most of the drivers and you will need just the graphics updated, yes.
4. you should unplug the current hdd while you install the new os and plug it back in once everything is set. you can then keep the data on the hdd or delete some of it or format it all, it's up to you really.