If you think to do the job is so easy than you do it, but the panel builder know for sure wat to do, has in stock materials to do it right, he know the law and regulation.
If you still think you can just order some components and asamble is a panel builder than do it by yourself, when it will burn the first one you will think more.
What I saw in the picture is verry busy place with components, from one of the top supplier of components.
By the way do you know the request of China for copper is so big – and the offer is not equal so the price is going up – true.
Wire now is 35% bigger than 75 days ago.
For components try another good example Eaton Moeller, with Darwin technology.