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

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.

I was to follow up on the Cable Type, Run Requirement, with a question about Containment. 

I witness miles of Data Cable being Installed it is usually laid in a dust controlled environment and is usually concealed under a Metal Clad Floor Tile with Screening Properties?

I was to inquire if a metal conduit would have any benefits for routing the Data Cable?