Windows 10: Blocking a program in firewall?

Yes, Comodo Firewall and particularly its sandbox, are the best defense, better than "the best" AV.
This person tests various AVs against ransomware, there are various results, but sandbox gets 100%.

Comodo Firewall against Ransomware - YouTube

I have never had single issue disabling it, store apps and everything works without it. But if you ever need it, you will get a message, that WSH is disabled contact your administrator, then you can just enable it back. A single entry and it makes a huge difference, there is also powershell and netframework malware spreading lately, but it also gets started via WSH, like Locky ransomware.

A closer look at the Locky ransomware

The rise of .NET and powershell malware - Securelist

 

You say you don't need a firewall if you have a router, so should I even have an antivirus, since I have a router?

 

PC can be fine without AV, but I would not go around advising people not to use it. People, who do not rely on them usually have other means to protect their PC. Like this poll shows, that 25% people do not need it. There are many factors, like what software you use, what webpages you visit, if you use services, which needs to be specially protected like paypal and so on. In the end, it is all about risk assessment. The only one, who can really answer that question is you. I have nothing to loose, even if I would be infected by ransomware, I would just reinstall, restore my backups and within 3 hours my PC would be like before. If you decide not use AV, you should perform on-demand scans time to time. Imaging and sandboxing is the best way to go. *Think

 

Here is a handy batch file for easily adding files to the firewall.

GitHub - charlesdh/addfwrs: addfwrs - created by Charles de Havilland