Your enclosed run sounds like a good idea, and would be more than big enough for your birds, plus a few more
You’re unlikely to have too much trouble with harrier hawks except with very young chicks - there are lots of urban legends about African Harrier Hawks going after pets, including cats and small dogs, but as a keen birder I can confirm those are just myths. Harrier Hawks are specialized foragers and their preferred prey includes bats, lizards, small rodents and nestlings, which they fish out of nests / holes and crevices in trees and cliffs. They have been known to take adult weavers/sparrows and even one record of a fully grown squirrel, but a grown chicken is almost definitely beyond them, given that they don’t have the short, powerful legs and stooping flight of a “true” raptor.
There’s actually a breeding pair of Harrier Hawks in our street, but but they’ve never taken an interest in the girls - the juveniles have given me a few frights though, as they look a bit like buzzards (which are major chicken predators) before they get their grey plumage
Sparrowhawks and Goshawks (and one very determined Genet!) are my main predators, and a few people in the neighbourhood have lost birds to them. One of my neighbours even lost some runner ducks to the local Goshawk female before she built fully enclosed runs for her birds.
If you do have a rooster, that will also be a big help once he matures - roosters can be excellent flock guardians and will sound the alarm to get everyone under cover if they spot danger. Some will even fight off predators like hawks!
Are you planning on adding to your flock? Sounds like there are some babies who will need homes soonish, and chicken math is definitely real