One colony has had three shallow supers and a 14 x 12 as a super. A super had been removed previously (and some brood frames had been 'borrowed' earlier, too). She was laying in two of the supers earlier on, but three were eventually just about filled with honey - the 14 x 12 was put on to achieve some good drawn comb as a first target, but they needed to be extracted as it was OSR in the frames. That particular colony has now been dissected and is in 6 nucs and the rest of the bees will be united with the original 'A/S'd' queen shortly, or used for another half dozen nucs, I am not sure which, yet!
So I would say you might be safe with four per hive.
Now, for some, 'this year's harvest' could be zilch.
With regards lifts, your colonies will likely need a double brood (or at least a brood and a half) or your crop may be limited by swarming activity rather than super space! That was why I discarded my WBC hives.
The better bet is seconds in the winter sales, but that would not help for this season. As you give no details of your present usage or colony history I would have no idea how many you might get away with this year. For instance, this year nuc starter colonies or productive stocks?
As RC says, some honey can be extracted throughout the season. I, for instance, have extracted as much of the OSR crop as I can, practically, and most now have the equivalent of a couple of supers on them. I don't expect too much from some, for the next few weeks, but they may need them later.
So, yes, the answer is a 'piece of string' really.
RAB
PS. Of course you could split any strong colonies and not need any extra supers per hive - just get extra broods and hive components!