His beef with China seems to be mostly economic, the trade between the two countries is too important.
The wall isn't that ridiculous - with the threat of potential terrorists entering the country as we are seeing in Europe, I would have thought you wouldn't want to take any chances by skimping on border security. At one stage Hillary even supported building a wall along parts of the border to stop illegal immigration, she is a massive hypocrite. Countries have to take whatever steps necessary to protect themselves.
His economic plan seems to be to take advantage of the historically low interest rates by investing in infrastructure hence creating jobs. Sure you might have to go further into debt to pay for it but if you invest in enough positive NPV projects, or at least projects with an IRR exceeding the cost of capital* then the country might have a chance of growing its way out of the current economic situation.
*Threw those terms in to see who is paying attention