I don't think this will help you @Tenegrief because of fixed times etc. but it might help others so have posted anyway, and hope you do not mind. The below is mainly about short-haul (Europe for me)
For popular destinations that you are "firm on" and popular timings, school hols, book as soon as they come out. They are unlikely to go down. Less popular routes ARE cheaper the nearer they get, but not when they get really close to departure. Between 12-2 weeks before tends to be the best prices for these, the week before you'd have to be lucky, the day before, not a hope. You generally cannot book "on the day", although sometimes through telephone bookings, and yeah, it won't be cheap.
Think about your luggage requirements. In the old days, budget airlines used to make everyone have the same option, but they do not now, so this is good. For a family of 4 it is usually far cheaper to book ONE big case checked in with one person, and 3 of you go hand-baggage only. Pros and Cons: Pro - check in and all done, no fighting for locker space etc. (not all flights enforce the bag thing once you are on), CON: you wait at the belt for it to come off. If it goes missing (not that often to be fair) then you have to resort to what is in your carry on packs.
Seats: Don't skimp if it really isn't going to suit you once you are on the plane, especially if you have kids. People are entitled to sit in the seat they have paid for. Some people might be kind to help you sit together, but there is no reason why they should, and the cabin crew don't like having to oversee the horse-trading. Other people treat it like a bus, no kids, don't care etc. if you are like this, don't pay for seats. You might end up in the middle one, but if you don't care, you don't care.
Skyscanner is good for finding cheap flights from multiple carriers (and as others say, sometimes flagship carriers offer prices that are not much more for better timings etc). Googleflights is better for long haul as you can set up an alert if the price goes down.
Do not underestimate the additional costs of flying from a different airport. You have to get there (train, parking costs, traffic etc.) and you have two choices - be brave and accept everything will work on time (then miss your flight when it doesn't, possibly losing accom charges), or build in contingency, which often means you have to stay the night before. It is fine if you have family to see, other sightseeing things etc. but if getting on the flight is your only objective, it can hurt if it goes wrong. Got to admit, with all of the train delays, it has caused me some stress.
Think twice about booking through a third party (trip.com , expedia etc.) to get a fiver off. It is absolutely fine if it all goes to plan. If it doesn't, cancellations, delays etc. then you will be the bottom of the list in the airline's view as their contract is with the third party. The airlines are not good to start with in these situations, but you will find communicating through a third party at weird o clock - nearly impossible. (there are exceptions when it is package etc. if get that)
Watch your insurance if you have made yourself "your own package holiday". I actually only buy it to protect myself against very expensive medical bills or death. The elements are separate - so to give an example, you fly with BA to AMS, to then fly on to Istanbul with Pegasus 3 hours later, where you have non-cancellable hotel booked. BA flight is 2.5 hours late and you miss connection. Pegasus don't care, hotel does not care, you have to pay the lot and other than the initial flight you have not a leg to stand on, some insurers will do dynamic insurance to cover this situation, but really does mean you have to work out whether you can do it. If you ever see the word "self-transfer" this is what you are getting *up to you to make the second flight buddy". As an alternative, if I had booked with BA to Istanbul (via AMS) then your treatment is better, basically they have to get you there. Can still be painful, but it is on them.
Anything airlines cancel within a month, probably on them, anything outside then you are faced with trying to adjust your plans including accom, or get a refund for the flight only. Wizz air particularly bad for this in my personal experience
Sorry for going on, and I have made it sound like an absolute minefield (I have flown 100s of times in Europe and 90% fine), and for you OP, your choices are fairly straight-forward, but just if anyone else comes on the thread, is hopefully of some help. xx