And… I’ll tell you here and now that achieving huge player counts is not done by a single computer or processor. You can up the specs of your PC but at some point you need scalability. For a simple explanation and even open-source code to look at and understand, look no further than the Minecraft bungee project.
I think you’re missing the point. If you don’t currently even have a game for people to play the number of people you need to support for your game, right now, is zero.
You need to make a game first before you worry about the number of users playing it.