Nighthawk C7000-100NAS AC1900 Modem Router Proper Optimization

Does anyone have any optimization suggestions for setting up the router?  I'm with Time Warner and because of the many devices we have connected in our home, we're getting low speeds even though we have 200mbps.  I know we won't get close to this with wi-fi, but we can't watch tv without seeing the rebuffering circle every few minutes.  Called Netgear and they want to charge a service fee for supporting their own equipment.  Um, no...so, I'm reaching out to the community.

Also, have a question about why my single network shows up as 5 when we look to change the internet channel because of interference.  There could be no other network on a channel I switch to, then, poof!  There's 5 all of a sudden.  Why?

Thanks!.