That is a heavy router. My Big Hitachi (about 1500 watts output) is only 5kg. I don't know what you have available in Iran but if you have to make your own, I would use about 10 mm thick. I have my Hitachi mounted to a homemade plate of acrylic that is 6.25mm thick and it is good. I only made my plate just large enough to pull the router from the table, a little smaller than you are suggesting. I also don't leave my router hanging in the table when I am not using it. I hope that helps.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.