Relay or mains priority circuit camper?

Hello, I would like to automatically switch the sockets in my self-converted camper to shore power when I connect shore power to the CE socket and, if no shore power is connected, feed the sockets via the inverter.

Since mains priority circuits are quite expensive, I thought I could implement this with a 230V relay with two changeover contacts. In principle, this does the same thing, if I haven't misunderstood.

Am I correct if I use this relay, for example: Eltako 22002601 installation relay ER12-002-UC (shown in the picture)

I would connect the RCD/LS combination device directly after the relay so that the sockets are protected regardless of the supply voltage.

1. First of all, the question is what would be the advantage of a mains priority circuit, does this also work with the relay?

2. The relay mentioned above has a rated current of 16A and a maximum switching current of 4A. Does that mean the changeover contacts can also withstand 16A? And the relay is controlled with a maximum of 4A?

3. Is my thinking about the RCD/LS correct?

4. Are there any points/questions that I may not have thought of?

Thanks in advance for helpful answers.