Hi,
1) correct
2) 10V @ 400mA = 4000mW = 4W.
Not the output power is rated for 250mW, but the power dissipation of the relay.
The ouput power = load power does not matter for the relay.
The power dissipation is Relay_out_voltage x load_current.
So when the relay is OPEN, then the voltage across the relay is 10V, but the current is almost zero. thus the power dissipation is almost zero.
When the relay is ON, then the voltage across the relay is small, but the current is 400mA. Again the power dissipation is small.
The coninous relay current is 400mA, so you are at the edge.
3)
3 Ohms at 1800 Ohms is about 0.17%, I guess the resistir´s tolerance is much bigger. Thus it does not matter.
4) max relay output voltage is 60V,
relay voltage input side is just 1.05V, the input never knows about the 10V, because the resistor limits the voltage.
Klaus