Can't I trap any adware/trojans at a network level using pfSense?
Not with PFsense alone, no. Remember, PFsense is a firewall distro, not a UTM. Are there creative things you can do to stop the virus from communicating back to its home base? Sure, like Stewart suggested…e.g. host file entries, DNS entries, domain overrides, firewall entries, etc, but that's not an effective or efficient way to fight an infected PC and none of those options actually resolve the infection.
As for using the "Reset this PC" feature of Windows 10, does that mean having to reinstall all my apps?
There's an option to keep your files, in which case I believe it will just re-install the system files and keep your apps, but from my perspective… why keep the remnants of a compromised system? Re-building with a clean environment is your best option IMO. Having to re-install your apps will still take less time than trying to thoroughly clean an infected system.