You can get away with two per colony.
But it reqires a lot of swapping about of frames and risk of swarming. One has to remove full frames and replace with new, so need some sort of transport box. Also need to do it often (very often!). In a good year for doing this, you may not get a lot of crop. In a bad year they will be overflowing by May!
How would I know this? My starting year was with 2 x National and 2 x WBC. Can't remember how many WBC supers I got but I do remember my mentor catching a swarm in his bait hive - it was probably mine as his garden was <1 km as the bees flew - and I started with two supers for the Nationals and I was soon struggling.
My Nationals did not swarm but I remember well - as that was the only year that I bought supers at full Th*rne prices and hurriedly assembled same! - that two was nowhere near enough really. After the OSR was finished I was OK with three, as I recall, but there was little forage available after the OSR, of course, as the bees needed to fly much further afield for forage.
So to recap, two might be enough if your forage is thin on the ground and spread evenly throughout the season; to cope you would need to inspect and change frames very regularly. With only two there is a much increased risk of swarming - think, strong colonies may need a double brood, let alone a complete home little larger than that.
Take PH's advice and go for 4 per colony. Maybe one or two less, in total, dependent on the strength of the colonies at the season start.
The alternative is to split the colonies into new broods (to reduce any potential nectar crop). So your original question has insufficient information, really. Apart from cost, having too many is tantamount to taking up the floor space of a single hive; not having enough is somewhat more annoying.
RAB
