Setting up 2 routers with one as a repeater

Hello community, (sorry if you receive this post twice, it looked like my first one was posted not in the U.S) I've searched different threads, and have not come across anything for this, or I haven't found it.
I'm looking to use my R6100 w/latest f.w as my router which is connected to CMD31T Modem. And I want to use my R6200 w/latest f.w as a range extender. Can anyone advise me on what settings to use via Netgear Genie. Upstairs I want to connect an X-box One S using a port on the R6200 and looking for some tips. Also my modem cm300... should I upgrade that with one that has 16x4 channel bonding?
Sq Feet 1500: Upstairs Xbox and Wii
Downstairs KFireStick, and then I have 2-3 lasptops, 4 -6 mobile devices. I realize I'm lumping 2 questions in here. Please advise. Thanks!!