Linux

A Thunderbolt cable will handle the required bandwidth from the dock to the laptop.

Your phone, do you expect to pass data via the phone and your laptop (eg photos/videos?) If you do then a USB 3.2 10 Gbps cable would be the most you would need (€25), costs may stear you towards a simple charging cable something around 60w (€10) would be ample BUT you phone may not fast charge due to Samsung's charging preference.

HDMI 2.1 would be ample for a your monitor (4k resolution at 120fps) and the cost difference between this (€13) and 2.0 (€10) is minimal nowerdays

Ethernet is easy, CAT5e in the colour/length of your choice would supply the potential max 2.5gb Ethernet port you have (€8 for 10meters). Higher the CAT rating the more costly the cable.

Additional Thunderbolt ports would be best used/reserved for high-speed external storage or even a gaming GPU.

The fact your asking about these items shows you should be pretty much covered for the next few years of 'fitire proofing'

Charging your phone through any usb port is fine, fast charging will only work with your supplied charger. USB-C adapts to supply the proper voltage. Beware of underpowering though.

DP is the best way to connect a high refresh rate monitor as it supports more bandwith. HDMI reserves a part of the bandwith for content protection. If you intend to use a 4k 120Hz monitor HDMI 2.1 is fine, anything higher I'd recommend DP. HDMI cables don't use the number spec, that's device dependant. To make it more confusing, 2.0b no longer exists and 2.1 doesn't necessarily mean the same on any device. Again, only if you need the full spec, for high refresh rate high resolution stuff, you need 2.1. Ultra High Speed HDMI is the best cable for that.

The ethernet port on the WD19 is 1000 spec, meaning it can do 1Gbps, or 1000Mbps. Cat5E, cat6 cat7 are all fine at handling that. If you intend to shrink the connector on yourself, make sure to pay attention to the order and if you follow correct procedure. Otherwise you might end up with 100Mbps.