1) Dont use 2 Antivirus programmes together with both in Real time protection mode. Enable real time protection in one, while using the other for the occasional full scan. You can beef up by adding free Malwarebytes and anti-spyware/ anti-trojans to your arsenal, but duplicating the AV wouldnt do much good.
2) Regarding MSE and Norton, I had been using MSE for a while now. I noticed while MSE is excellent in preventing infection, its not so good at actually cleaning up once the machine is already infected. Had this experience a couple of times, now have switched to Norton. Its quite lightweight though it has its annoyances- it insists on a browser toolbar, vets my google search results (with a green tick!) and generally is more intrusive than MSE. Lately it has been giving me infection warnings which I think are a false positive because that file doesnt exist on my machine. But otherwise, it seems to be working OK.