Don't defrag SSDs. You'll wear out the drive faster. And OS X, like Linux distros, doesn't need to defrag, as the file system organizes things automatically.
In terms of clean-up, you can install clean-up apps like Disk Diag and many others. However, some can do more harm than good and I suggest you just leave it be. The only maintenance you need to do is to delete rarely used documents, movies, songs, etc.
How is the MacBook starting to get slow? The SSD is the fastest currently of any laptop and the hardware is top-notch. And you have 16 GB of RAM! (As you can see in my signature, I have the same laptop and in my experience, is very fast for my use.)
You don't need "cleaner" or "maintenance" apps to keep your Mac running well, and some of these apps can do more harm than good. Most only remove files/folders or unused languages or architectures, which does nothing more than free up some drive space, with the risk of deleting something important in the process.
These apps will not make your Mac run faster or more efficiently, since having stuff stored on a drive does not impact performance, unless you're running out of drive space. In fact, deleting some caches can hurt performance, rather than help it, since more system resources are used and performance suffers while each cache is being rebuilt.
Many of these tasks should only be done selectively to troubleshoot specific problems, not en masse as routine maintenance. OS X does a good job of taking care of itself, without the need for 3rd party software. Among other things, it has its own maintenance scripts that run silently in the background on a daily, weekly and monthly basis, without user intervention.
Also no. The section you quoted specifically mentions hard disks and the article you linked to is 5 years old, before Apple started using SSDs.
Disk defragging is unnecessary for SSDs not because of how OSX works, but because of how SSDs work. HDDs are the only storage mediums that need defragging so that all files are placed at the front of the disk and the head has less distance to travel. The OSX file system did that automatically. No head on SSDs means no need for defragging. SSDs write sequentially starting at block 1, go to the end, and then restart so all blocks get written to equally (more or less).
Don't worry about wear and tear on your SSD. It's true they have a read/write limit, but for a 256GB drive you would need to write 6GB/s for a year and a half before the drive will fail. Saying the typical lifespan of a computer is 5 years it's nearly impossible for you to wear out the SSD before replacing the machine (you would need to continuously write slightly more than 1.5GB/s for 5 years).