I did Welp last year. Ordered 60, received 68. We lost some in the first few weeks to leg injuries (maybe our setup's fault). Then we lost some more to what looked like heart problems. Only 54 made it to harvest. In general I was not impressed by the genetics I was sent by Welp.
This year I used Myers Poultry Farm, which is an actual hatchery in PA. They come in next month so I don't have anything to report on the quality.
I feed dry grower in the first 3 weeks while they are still using the slide top feeders. When they transition to twice a day feedings I make a slurry out of the food and it definitely takes up some water and prevents the sneezing and coughing while eating. The general rule I follow for feeding at that point is what can they finish in 15 mins as a group.
Meaties are generally fragile but I have learned a lot over the years to prevent early death. It can be frustrating. Maybe get someone you know local to come by and have a look at your setup, another set of eyes might catch something that is causing your problem. I am better at feeding, raising, and nourishment; but hubby is better at setup intuition and bird safety.