Answers:
yes they shouldn't interfere beside respectively other. Wh is right, remember that the more programs that you own running the slower the computer will be. If you do not see a drop in show and you want to be "overly safe" than you should be fine.
Not a great belief. They will put away up your memory and slow down your computer.
Its secure but it will slow your computer down and more than potential single one is needed, I have two at one point...lately made my computer run approaching crap.