ETA: "I" wanted about 8 birds. The hubby "Farmer Hip Hillbilly" insisted on 40 citing "You're going to have losses for various reasons that is why I am telling you this number." Well, I have talked him down to 20 (the fight gets exhausting).
Of course, we were all new to it at some point. I started with silkies and we were surprised to only get tiny eggs

It's not right for anyone to try to talk you out of it just because you asked the same questions many people have. If you go to the feed section of the forum, Stormcrow has some good explanations of why DIY doesn't work out for most people. I'm most interested in how to keep our chickens going in some kind of disaster but it would frankly be a lot of work.
Tell your hubs that he is betting on failure and most people don't loose that many unless they do something really wrong. In fact, overstocking could lead to more deaths if the space isn't sufficient / disease burden / or you wind up taking risks with feeding (like free ranging despite predation).
Build everything to be predator proof and keep an eye out for signs of them when you free range and you shouldn't loose many. We haven't lost any to predators but a couple have passed for mysterious causes over the years.
It's easily solved by getting more chicks!
We have 40 growing out right now and it is harder than raising a half dozen. Just keeping up with their space requirements as they grow is a whole new learning experience for me after I've raised a lot of batches of chicks. Sometimes you walk out and they seem to have doubled in size overnight. I am calling one Popcorn for just that reason.