There are several ways to do this. The easiest is just to make your adapters set to MonitorAll and then set StartOnProjectStart to true. In your automation when you want to launch Chrome, instead of calling Start on the adapter, you'll need to use the Static Method Process.Start() available from the Global Assembly Cache in the System assembly under Process. Pass the path to Chrome.exe as the fileName argument and the arguments will be a list of URLs separated by spaces. You could concatenate the StartPage property of each of your adapters with a spaces separating them for example.
I don't know if I really have a strong opinion one way or another. I would always suggest using the adapters in the simplest way possible which would keep each in its own window, however since it doesn't really matter with the UWA, it is probably fine as separate tabs. As for performance, I don't think it will matter either way. Your challenge with the tabs though will be on restarting them should a user close one of the tabs and you need to re-launch it. I'm sure you could somehow launch it back into the tab group somehow, but you'd have to search for and test that solution, as it isn't something I am familiar with.