Hello again.
Yes, lots of things can happen with chickens. But the best prevention is proper housing, environment, feed/water and protection from predators.
So... my first piece of advice is to return the coop if you haven't already assembled it.
Instead spend this time trying to find a used shed or maybe you have your own shed on your property you can use and convert that into a coop instead. Most people know someone that can do some minor carpentry work to install a pop door, ventilation, windows and simple poop boards with roosts over them. Being able to walk in the coop to tend to the birds is so much easier than having to stoop over with a pre-fab.
Then you can install electric poultry netting for a pen connected to the coop, preferably with some shelter inside the pen, like a large shrub or something like that.
I'm not really old but I'm "older" and my setup makes it truly easy to manage my flock. I've only had one predator loss in their pen. From a hawk. I lost a young, inexperienced pullet.
It only takes me 15 minutes total from walking out the door to walking back in to change their water, feed them, turn them out and clean the poop boards each morning. That's it. Another 3 minutes in the evening to lock them up and do head count.
Feed them a complete diet and always have fresh clean water and keep the treats to a really low roar and you will avoid most issues with malnourished and overweight birds.
Give them a large run and they will get lots of exercise.
If you keep your flock size small, that will reduce the chances of health issues.
If you choose breeds with normal egg production instead of hybrids that have been created to crank eggs out like mini factories, you will avoid a lot of the health issues caused by reproductive tract failures.
Chicken are truly enjoyable, endearing creatures and I cannot imagine entering retirement without a flock. Don't give up. Keep asking questions. The more you read about these issues that have you concerned the more prepared you will be.