Um, I'm wondering how you know it was owls that took your chicks.....sounds more like something a raccoon would do. Anyway, I know you said you'd be moving the roosts, but if something can reach in, something can eventually get in. Personally, (and I know some disagree with me as often as I've repeated it here on the forum), I don't believe there's any such thing as a "predator-proof setup". The moment I start counting on wires and hardware cloth and whatever else I could come up with and start to relax, some predator is going to find a weak spot or a spot in need of repair that I've overlooked. All of the predator-proofing in the world does me no good if I get complacent and rely strictly on the measures I've taken rather than on my own eyes and diligence. That said, somehow you have to make sure that no little raccoon hands or weasels or the like can squeeze through the bars and there's only one way to prevent that - a good, solid layer of hardware cloth. I know there's nothing any of us can say that you haven't already said to yourself, so 'nuff said on that topic.
As for replacing your birds, please be sure you aren't exchanging one way of losing birds for another. Make sure that if you get new chickens, you get them from someplace reputable, and quarantine, quarantine, quarantine until you are 100% sure they are healthy and not going to bring in a virus, bug, or parasites to your existing flock. It would be terrible for you to have gone through the sad loss of chickens to a predator, only to lose the rest of them because of rushing into replacements.
I wish you all the best of luck, and I'm so sorry for your loss. I hope the advice you've been given helps you.
Problem with infectious coryza
2 seperate flocks on 1 property? Biosecurity issues? Other advice?
