Wifi drops and weak range.

I got a cm1200 that provides internet from ISP cox communications gigabit speed. Connects to a Rax80 multi gig router. Both modem and router can be aggregated but they are not at this time. From my router I got ethernet ran to a R7000 smart wifi router in garage from port 1. Seconded, from port two goes to Gs105 unmanaged gig switch. From port 2 on switch I ran a ethernet to my Ac1900 smart wifi extender. My extender is in the attic in the middle of my house. My router is in high corner spot in dining room. Both extender and router are 9-10' ft apart. My router is supposed to get 10,000 sq ft and the R7000 extender gets 2000sq ft. What em I doing wrong; for the connection to drop or having to go back and having to re-set complete system...what seems to be every two to three months it seems. Where I got to go through the whole system. Please help this is my first network that I bought.