Windows 8.1 (Pro) Win Update & "Add Features"

I received a windows 8.1 Pro key from onthehub.com after logging in with my school's info. I thought it'd be a good opportunity to get win8.1 Pro since it was free. So I receive the key, create a bootable usb using a downloaded disc image from Microsoft site and I install windows. Windows is activated, then I go to windows update and click check for updates. The status was stuck on "checking" for hours, and left it overnight. Next morning it did say 100+ updates were found, but when I clicked on install I got an error (which I didn't write down). I thought maybe something went wrong during the installation since I have multiple drives on my computer. I reinstalled windows and I noticed that windows update had the same issue. I tried checking for solutions online but to no avail. Then I noticed the add features to win8.1 option. I clicked on it, was prompted to enter a key, I assumed it wanted the same key again and whatever that was, it didn't work. I checked online again and by what I currently understand, it's an option to upgrade to the Pro version of windows from the Home version. If that's true then why isn't it working for me? Then I went to check the version by right clicking PC > properties, and it said 8.1 pro. It seems like I indeed have the pro version but then what's up with the add features option? This is basically my first question.

My second question is why does windows update take ages to find updates? I went on a different pc in our home and clicked on check for updates and no longer than 20 seconds later it says "6 updates were found". We're both using the same network so why does the other pc get a response and I do not in windows update?