I am wondering if this combo of anti virus and firewall is good ?

Sorry but you might have to get a computer if your PC only has an 80 GB HD! :P But You really don't have to defragment that often, once a week would be just fine. CCleaner works well to speed it up, but AVG or as like I say A Very Gay virus scanner isn't really worth it, try Panda, Kapersky or Avast. Format your firewall to work in tune with your other progams, I use Outpost. Make sure you don't run them constantly and at the same time, of course that will slow it down.