Hello feathered flock and welcome to BYP
The only possible problem that I can fore see is might be the ISA. They are notorious for being aggressive to new additions to the flock, however they do prefer to work in gangs so a single bird may be less risky.
Plymouth Rocks, despite their size, tend to be friendly, non aggressive birds.
The other ISA concern is they are unlikely to be as long lived as your pure breed choices. ISA and other commercial laying hybrids have an initially very high egg output. This puts enormous strain on their bodies an in their second season they often develop reproductive issues. They are also a very friendly bird so your daughter will also bond with the ISA - sad if it doesn't live long.
The best advice when establishing a new flock is to start with birds all of about the same age and at the same time and a minimum of 3 so if something happens to one, you do not have a 'lonely only'.
As Benen said, the rest is not accurate. If introducing new birds to a flock it is always better not to bring in a single bird and if there are problems we can help with strategies to over come them.
1 m square/bird is adequate but more is nicer for them, especially if one bird is very dominant. You can increase the available space in a small area by providing vertical layers (perches, swings, tree stumps and biscuits of lucerne for entertainment/activity etc) Management will be much easier for you if you are able to stand upright.