There will be an ISO, as explained in their FAQ page:
Can I reinstall Windows 10 on my computer after upgrading?
Yes. Once you’ve upgraded to Windows 10 using the free upgrade offer, you will be able to reinstall, including a clean install, on the same device. You won’t need to purchase Windows 10 or go back to your prior version of Windows and upgrade again.
You’ll also be able to create your own installation media like a USB drive or DVD, and use that to upgrade your device or reinstall after you’ve upgraded.
This change is for home users, and as far as I know, most home users already have automatic updates set on their machines. The only difference is that it won't be delayed to next Tuesday.
For those like me who manually check for updates every month or so, nothing will change. That is, as long as we can still decide which update to install.
Microsoft is in the process of doing just what cell phone providers did. Windows 10 will be free the first year. You can get Office 365 free for a year in so many ways. It won't be long before the switch is flipped, and you will be locked in to paying to continue using. There will probably be some changes made to file formats locking in you to using Microsoft to open files.
Not really. The offer expires after a year, not the upgrade. If you do not upgrade within that year, you'll have to pay. A subscription model was never mentioned.
"It's what you learn after you know it all that counts." -- John Wooden