The blog post is more of a warning to not use large "HD" images which might range from over-scaled sprites, to 4k backgrounds. In practicality you can have hundreds of different images(books, sock?, etc) at the scale you have posted.
What you should not do is have them all on one screen and moving at the same time.
Think about how you can swap out x many things that take up x memory for something else that gets you up to where you want to be.
There is no pre defined amount to recommend. You have to look at the target hardware, and what the current artwork takes up in ram, which is a little more than on disk.