So, there was a discussion in chat (and in fact, at the time of writing there's still such a discussion ongoing) over how much sense an SCP article needs to make, and how much weirdness it can have. The answer, infuriatingly enough, is "Exactly as much as it needs to." However, there are some guidelines.
First, understand what an SCP needs to do. It needs to create a strong impression on the reader's imagination. This can be purely visual: "That would look awesome and/or terrifying!" It can be frightening: "Jiminy Cricket! That sure scares the bejeebers out of me!" (Also, the reader is a young boy from a 1950's sitcom) It can be thought-provoking: "I wonder if… Huh. That would be weird. I guess maybe…" The latter is ideal, but the important thing is that there is some lasting impression that strikes your reader.
Now, clearly you want something pretty weird. That's the name of the game, after all. The question is, how weird?
If you add a weird aspect in to your object, that makes an impression. How much of an impression depends on what the weirdness is. Sometimes (I would even say most of the time), just a single bit of weirdness is best. SCP-426 has exactly one weird aspect. It's a doozy, but it's just a single line of strangeness, that the people around it use the first person to describe it. The rest of the effects are an extension of that effect. Of course, sometimes, you can combine multiple bits of strangeness. SCP-914 has two, if you look closely. One is the obvious, its ability to improve things. However, there's also the fact that it's nothing but clockwork. No real powersource aside from springs. It clearly [i]shouldn't[/i] work (even moreso than it already shouldn't work). That adds an extra level of strangeness that helps the idea of the article impact on the reader. So sometimes, bits of strangeness can combine to make a more effective SCP.
However, there are caveats. If you have too many different bits of strangeness, the article will start to lose cohesion. A flying platypus that lays golden eggs and has poison that cures AIDS and the ability to talk is… Well, it wouldn't really work. It's just a bunch of different, rather random effects. Plato the Platypus just isn't going to stick in the reader's mind that well. The effects don't knit into a solid core concept. Thus the Conservation of WTF. You want your reader to have that moment of "what the fuck?" However, you don't want them to do so too many times, or they're going to lose interest in what they're reading.
Now, how much strangeness is too much? That depends on a lot of factors. How good is the writing? Good writing can help disparate aspects of an SCP flow together more evenly, or even make the reader forgive certain excesses because they enjoyed reading the article. However, please do not assume your writing is that good. Gears can hardly afford that assumption, and you're not Gears (unless you are, in which case; Hi Gears!).
Then there's how well the elements fit together. This is more of an intuitive fitting, you understand. When your reader goes through your article, do the various bits of strangeness fit the "theme" you've come up with? A firebreathing duck that emits corrosion? Doesn't really work. A rotting corpse that hunts people through a pocket dimension? Fits the theme and the image the reader gets much better. Good writing will help with this.
Another factor is the scope of the piece. This is partly length, but largely… The size and the impact. For one of the more extreme examples, look to SCP-093. There's a lot going on in that article and its supplements. It moves on its own. It changes colors. It induces feelings of calmness or depression It rests on mirrors. Oh, and it lets you travel to an alternate reality. And what an alternate reality it is. It's probably one of the most complex SCPs on the site. But it works, and it works because of the scope of the SCP. An entire other universe! With its own backstory. The writing helps smooth things over so that after you get through the initial effects of the object, the universe knocks you on your ear. But done skillfully enough that it all draws you into a narrative.
Of course, your SCP probably won't have that scope. I'm not saying it can't, and I'd love to see more SCPs with that kind of ambition, but it's hard as hell to write something that big without devolving into a mess. You have to start with a big idea, and write it up well enough to make everything fit together. By the time you finish 093, even though you're left with questions, you still have an overall feeling that everything fits together.
As for how much sense the SCP needs to make… The Foundation needs to understand what an SCP does. They do not need to understand how it does it (or even what it is, necessarily). So focus on that. Focus on what tests the Foundation is able to undertake. You as the author may or may not have answers to these questions, but you don't need to give them to the Foundation. Contrariwise, if they could perform a test, and you don't have an answer, come up with one (or at least hint at one). Decide what it's reasonable for them to have figured out, and make sure that's in the article. Then see if it still gets your idea across. If not, you need to add more information, find ways for the Foundation to have learned it.
So, to restate the first answer I gave, "Enough weirdness and sense, and no more, and no less." Every article can support a different amount of weirdness, depending on the themes, the scope, and the initial idea. If you start adding more than that, you'll lose your reader's interest. You don't need to understand everything that an SCP does, but you need to figure out as much as the Foundation would know.
Like all literary advice, these aren't hard-and-fast rules. They're generalizations. Finding the right ratio of WTF to explanation is an art, and you have to feel it out. But if an article isn't working, sometimes you just need to step back, and ask, "Does the rabbit really need two brains?