If I start replacing my HD boxes with the wireless 4K Xi6 boxes will it affect....?

my ability to stream movies and sporting events without buffering.

Let’s say right now I have 4 HD boxes, but I upgrade all my tv's to 4k. If I get these Dolby vision capable Xi6 boxes, I see there is no coaxial cable port and I have to connect the box either with an ethernet cord, or wireless to my router.

My thought is that I may run into potential problems down the line because these boxes are taking up my modems/routers "bandwidth" in a way the old fashioned boxes never did via the coaxial cable connection.

I'd like to make the leap to all 4K boxes, but I certainly don't want buffering or pixelated video as a result of anything in the chain getting overloaded.

I am aware that using these boxes to watch regular cable channels or "on demand" does not count towards any data cap, but since I am connecting via ethernet (or wireless) it tells be that something is being routed through my router, and I would appreciate clarification.

Thank you