I want to replace the router/modem Comcast with a high quality for streaming

@mitch2 “…that will hopefully provide the speed I am paying for. ”

Good luck with that. Bird dogging Verizon to get what you pay for is a full time job. When you don’t get it with a third party modem / router they will claim it is your router. 
 

Don’t get me going.

As strange as it might sound, this is a real Newbie on such an area of Data Transfer. 

How many Cat 6 or above Cable Runs is sensible planning? 

@ghdprentice - Xfinity just left after helping integrate my new Arris SURFboard T25 DOCSIS 3.1 Cable Modem, which doubled my internet speed over what I was getting with the previous modem.  Speed Test showed well over 500 Mbps now, which is certainly all I need for my home usage and which was well worth the $112 cost.

@pindac 

When doing a major renovation a few years ago I put in flexible plastic conduit with pull strings inside to help future proof the installation.

@mitch2

Glad to hear it. See how long you have that speed.

Xfinity would not touch my Modem / Router.

Also check your billing for extra charges. They charged me $100 to put in their router and a couple mystery charges. No cost other than the monthly charge told to me by the technician.