Kana is not all that complex. I learned it in the course of one semester (so about 3 months). Kanji is the real stumbling block. There are 2,136 jouyou kanji - those that are considered to be common use and are taught in primary/secondary school. You need to know somewhere in the neighborhood of 3,000 to be able to read a newspaper, and there are something like 10,000 (50-100,000 by some estimates) total kanji in the language as a whole. The good news here is that a lot of the “uncommon” kanji are things like people’s names and what have you. Since they are recognized as being uncommon, you’ll typically get furigana (small kana to show you how to read them) to go with each kanji.
The short version is that there are “only” 2-3,000 kanji that you would be expected to know. Still an uphill battle, but it is made significantly easier if you’re in country. I found that the daily exposure did more for my retention than any amount of study time I could ever put in.
-CK