How big would the new space station be? As big as the ISS or even bigger?
No, smaller. A few modules.
But it is not going to happen. The Russians are having major problems. They have had a laboratory module to launch to the ISS that has been in trouble for almost a decade now. They discovered contamination problems in the fuel system back in 2013 that they still have not fixed. Take a look at russianspaceweb.com for details. It's a big mess.