A lot of those memes are probably the same image. Would it be possible for Imgur to remove duplicate images and just redirect users to the original? That might help save bandwidth.
If you delete it as soon as the user comes online, wouldn't their information be safe? No one else would've been able to get the information because they were offline, right? And so it's not still saved if the user exits the webpage before they return online, you can use SessionStorage.
If I understand you correctly you're saying if I'm working on my own project go with Contentful? Also would I still be able to use WordPress plugins if I'm only going to be using WordPress for it's API?