1) There is no way to separate the Electron engine from your app, so you have to bundle Chrome and Node with each app.
2) Electron has an autoUpdater API, but since Electron doesn't solve the installation/updates problem e2e (packager + installer + updates server) it's really a half baked solution. This is specially bad in Windows since Squirrel for Windows is in my experience a disaster.
I have a number of Electron apps in production, internally and for our customers, and for our next desktop project we won't be using Electron.
The idea of using web technologies for the UI is still very valid IMO, but considering the 2 previous problems it's way less of a headache to just make our own native wrapper in C# and Swift (sorry Linux) and finally distribute the app via the official stores. At least for our use case.