I'd definitely stick with just one, to work on your reads, and knowing how to play all hands well from all positions. The action will be too fast for you to handle multi tabling, and in the long run you will suffer from it.

I only single table $3/6NL because most of my play depends on reading people. Giving that up puts me in a position to not make as much. Sure, it can be a bit boring, but I'd rather be bored while making money than excited and losing money!