Theoretically, you could do that by exporting IP ranges from geoip database. However, generally, this will not really solve the problem, at least not completely. Besides, adding many iptables rules (>1000) will result in an additional load on your server.
I think something like that can be done through cloudflare, in the security settings
You can. The only issue, however, is that our country block is not a full block. It would present a captcha page to visitors & a human visitor could still enter the site (really designed to help stop bots). We will likely make this capable of a full block next year.