Hangul was actually created to be a written language for the people. You are correct there, before the commissioning of Hangul in 1443, the Korean people used primarily Chinese characters. But now and since then, Korea uses Hangul as their national written language. When you travel around Korea, you will see primarily Hangul characters, although there is still alot of evidence of Hanja or chinese writing.
You are right there as well, Hanja is simply what chinese writing is called in Korea. You are also right that the average high schooler must learn the 1800 "basic" Hanja characters. Middle schoolers, about 900. Although I wouldn't necessarily say that Hanja is the written language of the educated. Many advanced text books are written almost exclusively in Hanja...especially medical references and very high level scholarly works. In fact, most newspapers even have some evidence of Hanja in them, but generally only from those 1800 basic characters.
Interestingly enough, as it impacts us, if you get any Korean martial arts text books, you will find a great deal of the words in Chinese. Basically, the explanations of movements are in Hangul, but many of the movement names and especially "area" names are in Chinese. This is because a lot of our words are taken directly from China. For example (at least in Tang Soo Do), Choong Dan Kong Kyuk is the Korean for Middle section punch. If you find that in a Korean MA book, all of those words will be written in Chinese, making translation very interesting! Especially since Hangul takes a few hours to learn, but Chinese can take YEARS to even get a basic understanding.
But, in short....the majority of Koreans use Hangul almost exclusively. In fact, many of the Hanja words are being written out in Hangul now. Hopefully I answered your question! Let me know if there is anything else!
