If you're getting a new PC, why going with W7? Default Windows Defender on W10 today is as good as other commercial antivirus, even better, with less "rubbish" which other antiviruses stick on your screen. If you're a little careful you will not need anything else. This is how I do on my laptop and haven't got any viruses yet. Google it for reviews and comparisons.
Raspbian on the other hand, is a fork from Debian intented to be used on Raspberry Pi's so it is equipped with software for ARM architecture. If you're switching to linux try something more user friendly and yet lightweight, for X86 architecture, such as Mint, Lubuntu, Xubuntu, Peppermint, or Lite. They're all Debian forked distributions for desktops/laptops.
I love linux and I am using Debian the latest 10 years. I would suggest to try Debian directly, but you might be a little dissapointed at first because it is not very user friendly or nice-looking.