@shaio 

1. The Deco units can connect to each other either by wireless or by wired cable to build up a mesh wifi system, so you can connect one satellite Deco directly to the main Deco by wired cable and others connect to it by wireless.

2. It is suggested to connect modem--main Deco--switch--slave Deco. We need make the main Deco works first, so that the devices connected to it or the switch can access internet; with switch connected to the modem directly, there is only one device  can get internet at once with the public IP address. 

May it help and have a nice day.