Sounds like you might have created a bit of a problem for yourself there. If any of those flights you've put in placeholder dates for have under a 24 hour stopover then it's a connection and you'll have to pay the $125 fee to change them into a stopover. Ideall you do that only once after enough time has passed that you have more room to work with.

But as far as just the date changes go, wait a while until more of the calendar has opened up and change all of your later segments to the end of the calendar until you're more clear on when you want to fly, then move them forward to the actual dates you want to fly. Date changes alone are free, so you can do that as needed, just so you don't have to change a connection to a stopover. Since you're finishing your trip in August, that's when I'd look to make the initial date changes, so then you can move all of the flights after segment 2 or 3 to August in one batch. Unless you have your dates planned already of course.

If the base fare changes in the meantime you'll need to fly the first segment before doing much of anything to the ticket. I believe you can still do date changes without refaring, but any changes to ticketed points (including connection to stopover) will trigger a reprice to the new (very likely increased) fare.

Another thing to keep in mind is married segment availability. Any connections you have are likely married segments, meaning D availability is different on the pair than the individual flights. QR and QF are notorious for limiting married segments on D fares closer to departure date, so definitely best to set dates sooner than later (but 4-6 months is plenty, I don't mean you have to rush as soon as you're at 330 days).