After the Clip Zip, the manufacturer of the computer chip used in the Clip players discontinued the chip and so SanDisk needed to do some strategizing for the future. Unfortunately, it went for an alternative chip–used by other player manufacturers as well–that just isn’t as robust as the old, crippling the capabilities in the Sport and Jam players.
Recommended, if you want to be able to play aac files: get the Clip Zip, which has that capability (although sometimes with hiccups) in the original SanDisk firmware. Even if you will be installing the alternative Rockbox firmware, which can play aac files, I think that it is beneficial to have that capability in the original SanDisk firmware as well, in case you want to use that capability. Again, see the linked-to review above with regard to the differences between the Clip+ and Zip players. I generally have seen both recently in the $50-$80+ range–higher than I would like, but it’s supply-and-demand for a discontinued player. Interestingly, this is around the original cost many years ago, when the players first came out.
Also, note that Rockbox can be installed on the Clip, Clip+ and Clip Zip players, but _ not _ on the Sport and Jam players–and so avoid the latter 2 player models if you want to use Rockbox and its mega-sized file-handling and database capabilities, which you seem to want.
As to the microSD card, see my recommendations above. Amazon.com is a good source, with good prices and a nice return policy.
Finally, installing Rockbox is relatively easy–Rockbox has an automated installation software utility. One need not be a computer guru. Again, my recommendation is for you to go to the Rockbox website and skim through the manual for the Clip+ or Clip Zip (again, don’t let it intimidate you). There is a section on installing Rockbox at the beginning of the manual–that should answer many questions. And then, once you do install Rockbox, download a “theme” you like (that’s the appearance of the screen) from the many available at the Themes webpage–you can even create your own, if you are so inclined (yes, it really can be done, spoken by someone who has done so–and my progamming days are from long ago!).