how to get the most out of my setup?

ok so here is the situation. my house consists of 4 people, 2 children. the 4 adults use an average amount of devices that use wifi, nothing crazy though. my room is attached to the garage as it used to be part of the garage untill we closed it off into an actual room. The walls are thick, and i have horrible wifi in here, even tho the router is right on the other side of the wall. On the other side of the wall is the "man cave" and right outside of that room (no obstructions, clear path) you will find our router/modem. distance wise ,the modem is about 30 feet from that first router.

the modem/router we have is a "wireless cable gateway CG3000D"
- currently have SSID broadcasting OFF
-DHCP server ON

the first router is a WNDR4500 v2 connnected via ethernet cable.
-DHCP server OFF
-no other settings changes.

I purchased another router on black friday because it seemed like a good deal, and connected it to the others by getting the cat5 ethernet cable coming from the modem/router, and connecting it to a netgear 5-port gigabit ethernet switch 10/100/1000. Then , one ethernet cable goes to the first router, and another travels up the attic, and down into my room which is connected to the new router, which is a Netgear AC1750 smart wifi router. Now i dont know how i should have set this up exactly, but something isnt right. My macbookpro on ethernet connected to the new router, drops connection alot. takes about an hour to download a 3gb linux distro. i believe i set it up as a seperate network , not an access point, but then i did try access point and still was shaky. It is not our service through cox, because speed tests were constantly giving me 45mbps prior(outside of my room).

please let me know if theirs something wrong with my set up,, or things i can do to increase performance.