[NAS542] Network config / best practice?

The ports can be trunked, but then your switch has to trunk it's ports either. A simple switch cannot do that, you need a managed one, which supports trunking. In that case both 1Gbit ports are combined to a single 2Gbit port.

Without having such a switch it doesn't make sense to connect both ports to the same subnet. While it works, it will effectively use only one port.

You can, however, connect each port to a different network, for instance your 'main' LAN and an IOT LAN. In that case your IOT devices can use the NAS to store/read data, but still cannot reach the LAN devices which use the same NAS via the other port.

In most cases I think it's wise to keep it simple and use only one port.