Two would be quite happy - until one of them died, leaving a single hen on her own. It's always difficult to introduce a single hen to an existing pair, or conversely, to introduce a new pair or even another new singleton to a single, older bird who feels in charge of the territory. Much best to equip yourself with a run and coop big enough for 4, and then get 3, so when in time you go down to 2 because one has died, you can get a pair of younger new ones. This also allows for the inevitable development of Morehens disease, of course.
Leghorns and Columbian Blacktails are among the smaller types. Both are pretty, very good layers, although leghorns are usually quite flighty and prefer a covered run with a high perch to fly up to. Cream Legbar hybrids, often sold as Columbines, are small and neat and the bonus is their blue or green eggs.
Bigger ones include all the highly -productive ISA brown hybrids, which end up as exbatts if they're lucky, Speckledys, and hybrids based on Sussex or Marans crosses. Most hybrids tend to be smaller than their purebred ancestors as they're bred for egg production and it's more economic to breed a small-bodied bird who lays well, rather than a heavier, hungrier, dual purpose bird who is also bred for meat. But they all need the same amount of space, as the smaller, flightier ones may be more active, at least whilst young. And if you plan your setup to house medium/larger birds, you can always get smaller ones and change to bigger kinds in time, if your tastes develop. If you stick to hens and don't want a cockerel, most will be docile and friendly and easily tamed, since they're bred commercially for living at close quarters with many others, where aggressive tendencies would be a disadvantage. Hens aren't usually aggressive to humans, or to each other once they've established the flock pecking order and know where they stand in relation to the others. You may get injured accidentally - this afternoon I got a long and nasty scratch down my arm when an over-enthusiastic pullet jumped up to investigate the treats bowl I was trying to carry in to the run- but this wasn't aggression, just carelessness on my part for not wearing a long-sleeved shirt. You also need to learn how to pick up a bird and hold her by the legs, so she can't scratch you. They soon settle down if held correctly.
The most important thing is to get healthy stock from a place which looks clean and spacious, and where you can see that all the pullets are active and interested. Nearly all of them will have been raised in a large factory environment, and the seller will have bought in a mixed bunch at around 16 weeks old, already fully vaccinated at intervals whilst they were chicks and growers. You're more likely to get long-lived and healthy birds from what is basically a commercial farm outlet, than from a smaller breeder who may have a smaller gene pool and possibly some inherent, inherited health problems in the stock. There are of course exceptions, but for a first-time poultry keeper it would probably be a good idea to stick to common breeds of hybrids and avoid small back yard setups and unvaccinated pullets, when buying your first birds.
