What's the Best way to network a PC and a Mac?

Downstream of my Xfinity cable modem, I have a NetGear RangeMax Duo wireless N-router, model WNDR 3300, set for WPA2 security, that manages access for two home computers: (1) Win7 Pro 64-bit Laptop connected to the wireless router via Ethernet cable, and (2) a Snow Leopard OSX 10.6.8 MacMini also connected to the wireless router via Ethernet.
My router and both computers are set for WPA2 security, and the router only allows devices to connect, whose MAC addresses I have entered in my router's settings. Both computers' native firewalls are turned ON, and I'm using Malwarebytes Premium v3.1.2 on the PC and Sophos Antivirus on the Mac.
I want to be able to share both computers' files ONLY with each other, being absolutely certain no accidental outside access is permitted to the files on either of my computers.
Rather than use "Public Folders" in this sharing setup, for seamless working purposes, I want to share all contents of both computers with each other, with each computer able to see its counterpart HD as a permanently mounted desktop icon, with all HD contents read/writeable from either computer.
I've looked at the complicated Windows workgroup, file sharing and network discovery dialogs, and the equivalent Mac OSX dialogs. All are daunting, and various online posts on how to share files between an PC and a Mac, seem to only raise new questions even as they offer answers.
Is there a 'best and simplest way' to achieve my goal of assured, secure, seamless sharing between my PC and Mac, with a permanent desktop icon on each computer, pointing to its opposite counterpart, giving each computer complete access to its counterpart's file system, while totally preserving security from outside access?

Trying to share the whole drive is hard and dangerous as it gives any malware Ransome ware access as well. A lot of folders on Windows have security set for system and users folders by default have deny to ADMIN even on the local PC. It's safer and simpler to just share a folder

Good advice; I should have more clearly explained that the intended sharing would be limited to just cross-sharing my User folders on the PC and Mac only, which would include cross platform sharing of all user Documents, Pictures and Music folders, etc. There would be no point in sharing system, applications, libraries, etc.