Hey @Wuurbz each Boost system starter pack should come with two units. Once you've downloaded the app and logged in, you can connect the first booster unit to the modem (this first 'master' unit remains hardwired after set up). Then you can follow the instructions you were given to rename it, etc. Additional units can be then placed elsewhere and should only need to be connected to power, and of course also connected and named in the app.
Yes, if you've got the WiFi Hub Gateway, it technically acts as the 'first' booster. Then, what you'd do is connect a boost unit into any of the yellow LAN ports of the Hub, connect to power, power on the boost unit and wait for the light to turn blue for a minute or so, and then you can disconnect it and place it elsewhere.
If you keep additional Boost units hardwired, they will have faster throughput, as they don’t need to store and forward each packet in each direction.