I am planning to set up a mesh system in my home using the Deco E4 but I am stuck with a problem. 
 I have an ISP's router in the middle of my house, right next to it I plan to set up a deco unit as my main router. From that center location i have ethernet cables in 3 separate areas (separated by concrete walls so signal is barely 1 bar)  to which i plan to star chain the routers to create my mesh. Problem is i am not sure of which router to use as my main router as there are only 2 ports on the back of Deco E4s which i already have. Any help will be appreciated. Thanks.