If I recall correctly, you do not need any wired connection to the router to make this setup function as long as you're not trying to deploy surrounds with the Playbar/Sub. All units can be setup to communicate via WiFi, though an initial temporary connection is required for the first device in the system.

Of course wired is always best, but if you can only wire one device in the system, make it the Playbar, which can be configured as a bridge/boost and has better RF propagation than Connects do. This way you'll have the option of using SONOSNet instead of WiFi.

If wiring the Playbar isn't feasible, I'd play it safe and add a wired Boost and be done with it. The Boost is the new version of the Bridge and has better RF output.