I disagree about it picking up off-flavors from the yeast after such a short time period. I think you would do fine to leave it in primary for 3-4 weeks, and you avoid the risk of oxidizing your beer doing a transfer. If you are planning to do a secondary because you are adding additional fermentables or something to that effect, it would make more sense to me.
shaffera, there is a lot of debate on when/whether to use a secondary and it really just comes down to a personal preference. You'll find lots of threads about this all over the forum. There is VERY little chance that you'll get any off-flavors due to yeast autolysis by leaving it in primary (Chris White and Jamil Z have done a good job explaining why this used to be an issue and why it is no longer), and the yeast is very good at cleaning up other off-flavors from diacetyl, acetaldehyde, etc with adequate conditioning time.
The best way to know when it is done fermenting is to use a hydrometer. Once it has reached a steady final gravity (gravity doesn't change for 3+ days), then give it another 2 weeks to finish cleaning up and then prime/bottle or keg it.