My own DH went through a big career change recently. He said the first few months on the new job were contant hyper-ventilation-verge-of-panic for him. It's like running uphill. I hope your own DH realizes that the learning curve for a new venture can be steep -- so it is like running uphill. But he wouldn't be there if he isn't qualified, capable, and ready to do it. I hope he cuts himself some slack. He'll do fine.

Wishing him a smooth trip over the hump and smooth sailing from here on!