Bandwidth is the easy part
Budget 25 Mbps per 4K stream and remember that it must be sustained, not peak. A speed test that hits 200 Mbps for eight seconds tells you very little about a two-hour game.
Test during the hours you actually watch. Neighborhood congestion is the usual reason a connection that looks fine at noon fails at nine.
The device has to decode HEVC in hardware
4K live streams are almost always HEVC. Software decoding a 4K HEVC feed will overwhelm any streaming stick, so hardware support is not optional.
Fire TV Stick 4K and 4K Max, Apple TV 4K, NVIDIA Shield and current Android TV boxes all qualify. Older sticks do not, regardless of what the marketing says.
The cable and the TV matter too
You need HDMI 2.0 or later and HDCP 2.2 for protected 4K content. An older HDMI cable or an unpowered splitter in the chain will silently drop you to 1080p or produce a black screen.
If 4K content plays as audio-only or black, suspect the HDCP chain before the provider.
Most live channels are not 4K
This is the part marketing pages leave out. A minority of live channels broadcast in genuine 4K; the rest are 1080i or 720p upscaled somewhere along the way.
So judge a service on how good its 1080p looks, because that is what you will spend nearly all your viewing hours watching.