If you book now and they implement new fees later, you are grandfathered in and don't have to pay them (for example for checked luggage). If it's a good fare, book it!
This isn't true at most airlines

As for cancelled flights, the airlines announce them months in advance, their schedules are already out for october. Cancelling a scheduled flight means laying off or reducing many schedules for many employees from ground support, pilots and air hosts. This isn't easily done and they always give a lot of notice. There are cuts in flights to Asia this november, they were announced in June. That's an example. Hopefully none of the airlines experience a catastrophic failure.
If you find cheap tickets, just buy em and dont worry

Ditzy, quite a few airlines do assignments when you check in. Southwest's method is infamous, I wont go in to too much detail. Which airline are you with? I dont think any that use this method gurantee seats together, I actually flew thursday and the family coming back from disneyland was completely separated, you'll have to get there and get a seat, but thats not hard generally, you do it on check in on the computer check in, there'll be a picture of the seats available and you touch the ones you want. Some airlines let you do this online 24 hours in advance. If yours is one of these, make sure you do it, or you will definately be split up as most people do check in and seat selection from home. If its not, arriving in a decent amount of time, 1.5 hours or so before your flight, is usually sufficient, but 2 is safer and what they reccommend.