You need 6 for the most popular sets, so I would say the first 6 you can find or buy. Sure there are some good sets you can make with less traits. Infused and Bloodthirsty would be good to have earlier rather than later.
However, the first 3 should be Arcane, Robust and Healthy simply because those are the easiest to find. Then you can at least make Seducer and Torugs. If you have the Mats, and or Material Passives to make them in the CP160 level....
You know, the mat chase alone is probably going to take longer than learning the 6 traits would.