100/100 is absolutely sufficient for 4k + guests, however what can happen is if something is consuming all of the bandwidth, like a very large file download (A 4k stream won't) then other users could notice slow or slightly unresponsive connections.

The solution to this would be QoS (Real fq_codel qos, not the stuff they call QoS in Netgear/other routers), which you can do with something like a Ubiquiti setup, which requires a bit of learning.

I'd just get the verizon one and see how it goes, if you run into poor performance then you can look into the options for getting your own router with QoS, and either putting the Verizon one into bridge mode or replacing it entirely if they let you.