"...a dock to simplify the task and to eventually also host some kind of solid state storage..."
If you were intending that the storage (NVMe?) should be within the dock itself, then at the moment the TB4 specification only allows 10Gbps of data bandwidth to internal NVMe SSDs.
Full internal speeds may come with future TB 5 docks...
TB3 docks can house a full-speed NVMe SSD internally, but they can only support one 4K/60 DP/HDMI monitor.
Unless its a USB-C monitor connected to the second, downstream, TB3 port.
If you want to use an external SSD, plugged into the dock, then any TB3/TB4 dock will be fine, so just choose one with the ports you need.
Remembering that TB3/4's 40Gbps bandwidth (<32Gbps for data) is shared by all the ports.
An advantage of using an older TB 3 dock (not TB4...) is that it has its own USB 3.1 Gen2 controller in the dock, which can work much better than the Mac's own USB 3.* controller with SSDs that tend to disconnect randomly.
Plugged into the dock, these SSDs/encolosures are much more likely to be stable.