Well, I don't think any of these really matters if you are just using a PC for trading because all you need is a browser with an internet connection.
The security does play a role if you are storing your coins in your PC because you would want to protect your private keys with higher security.
Any PC would do fine. I use an intel i3 laptop with 4 gigs of RAM. I don't use a VPN, I just use a hotspot from my phone and without any antivirus for my own reasons.
It does really matter for some people because trading with your own Laptop or PC is totally different when you are on a mobile phone unless if you are a kind of person who do always travel then you wont have any choice but to trade up with your phone but its always been preferable to trade on a pc because its less hassle when you put up some indicators or making up some side research and making some plotting which you cant done this things or too hassle when you are on mobile.About anti viruses i dont mind too much though since its always been updated and im not fan on clicking any phishing links.