Does giving out an IP address give someone full access to my computer and files? Or will they not be able to get through my router and software firewall?
Your IP is like your street addres. If you windows and doors are shut and locked, no one can get in right?
They would have to bypass the windows and doors...and to do that they'd hit a wall...literally.
Keep your computer patched with the newest versions of your software, install service packs for windows and office, and keep going to http://windowsupdate.microsoft.com
. Don't forget to upgrade your router's firmware as well, from time to time.