WeChat doesn't have an equivalent in the US. Everyone in China uses it, even old people. On the surface it's a chat app but it's also integrated with payment systems and mini apps. It's very common for a restaurant menu to just be a WeChat mini-app, I think even customs does their border forms via WeChat.
HSR between Shanghai and Beijing is a good call most of the time, only 4 hours and a well travelled route with frequent service. Helps that both cities are very much worth seeing.