Size your surge arrestor to whatever the maximum input voltage of your inverter is. 1kV on a 500V input is going to be OK but 800V would be better.
For the MCBs, again look at the maximum voltage you are going to use and go over a bit, those 1,000V DC units would be good for pretty much any domestic level string inverter.
You can use the same ground for everything, if you have a metal support structure (like our car port) bond to that.