Unfortunately the link you posted leads directly to the site's main page. However, judging by the URL, you're looking into a Dell brand computer. From my personal experience, I would highly recommend not going with this brand. Their computers are cheap for a reason, and it is not a good one.
That being said, have you considered building your own system instead? Generally it can be cheaper, gives you more options, and can often be much more powerful than anything you could buy at the same price.
As for the form factor, microATX is becoming more and more popular these days, especially in "HTPC's". (HTPC = Home Theater Personal Computer). Modders especially love systems in this form factor because they can place the equipment in very small places, and even make the computer itself appear as a standard piece of home theater equipment. (For reference, the standard form factor for most systems is ATX, although most pre-built systems tend to modify this with their own proprietary designs and parts, leaving you often very screwed when you want to change things out).
Leaving your PS4 on top of the computer should not be a problem, granted that you keep both clear of any dust, and neither gets too hot. Since a PS4 is basically a customized computer, it shouldn't have any issues being near your system.
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