Question... should I book when flights first open up or monitor flights?
Start monitoring now. Either get an online company (google flights, hipmunk, etc) to track rates for you, or build a spreadsheet yourself.
The hard part is knowing when to pull the trigger. NO ONE can tell you with any accuracy when this will be. Don't listen to the people who say "I always get the best prices 7 weeks out" or "It's always cheapest when they're released." When your flying (both time of year, day of the week, and time of time) affects the price. The departure and destination airports affect the price.
My best suggestion is to start tracking the prices. The legacy airlines should have their flights released now so you can start looking. That doesn't mean flight times/connections won't change. At minimum, look at prices at least every other week (check on different days also). At six months before your flight, if you haven't booked tickets yet, start looking weekly. At four months before your flight, start looking daily.
The airlines have gone to "no change fees", at least for a given time. You'll need to look and see what happens if prices drop after you book. Can you change to the lower fare? What happens to the difference (I'm guessing a credit, but not sure). How long do you have to use the credit?
Assuming you can get a credit if the fare drops, keep stalking that airlines fare after you book. If you can't get a credit, stop looking at prices after you book. However, periodically (start with every couple of weeks, then once a week, then daily as you get closer) check your flight and make sure the airline hasn't made a change. DO NOT COUNT ON THE AIRLINE NOTIFYING YOU OF A CHANGE.