I found a decent ticket, 12 hours, direct from YVR to NRT, for $1200 CAD. Thinking I should snatch that up.
$1,200 CAD should be considered a reasonable round-trip price from North America to Japan. Sometimes you see lower (though rarely below $1000), and sometimes much much higher. I would say that is around the average price these last few years, based on the flight price research I periodically do for myself or acquaintances making the trans-Pacific hop.
I always hear different things. Early? Late? Certain time specific to the season?
You likely hear different things because there are very few universally applicable rules to flight-pricing, especially for trans-Pacific flights. Sometimes the best price is six months in advance, and sometimes it is a few weeks - it mostly all depends on that particular flight.
I can say for sure that the most expensive time to fly to/from Japan is the New Year's season, the first week of May (Japan's "Golden Week"), and the middle of August (Japan's "Obon" Festival of Lights). Scoring an average-price ticket during these times will be harder than most other times of the year. However, September is not an unusually busy season in Japan.
2) A friend may want to come with me by buying a ticket in 1 month from now. Does it sound like it should be OK?
I figure he probably can't get the seat beside me at that time, or maybe even the same plane
One month in advance is pushing it a little bit, but it is not unheard of to find a reasonable ticket only one month in advance. I advise buying sooner if possible, and it is very unlikely that you'll be on the same airplane (or if you are, your friend would have to pay a lot of money).