Spectrum Modem Compatibility

Hi all - I currently have Spectrum Ultra (400MB) and am using my own modem - a CM600 - and my own router - Nighthawk X6 R8000.

I'm upgrading to thier 1GB (940) service and want to ask if my CM600 will work?  They say I need Docsis 3.1 so my guess is no, and...

Will there be any issue using my Nighthawk?  

If I have to replace my modem in the future, that is fine and I will use their provided modem for now.  If I do need to replace the modem, which of the Netgear offerings would you recommend?  My house has 4 TV's (2 connecting wireless and 2 wired) and multiple devices including laptops, phones, tablets, and a main (wired computer).  Then guests.....

Thanks for any assistance.