I use the Pay for version of A squared Anti-Malware and AVG I believe both have full time protection but I could be wrong. On my old computer I used to get conflicts with them maybe because I had not configured them properly to run with each other. But on my new Tower I have no problem with them using Windows7.
I would say you do need something with full time protection for when you are browsing.it saves you from getting hit with downloaders if you open a bad site. I use both WOT and Link Scanner to warn me of bad sites which helps.But a few of the good sites that I have opened is when I have been attacked and that is where the full time protection kicks in and stops it. I would say probably One Anti-Virus and One Anti-spyware program with full time protection should be fine.