One more nuance... I use pen and paper to take meeting notes and then transcribe the salient points into the journal file.
About four years. I'm averaging around 10k lines per year in the journal, but I tend to separate large logs out into a separate file in the logs directory and then link to it from the main file.
I like the idea of a monolithic journal per year. How long have you been at it (if you don't mind me asking)?