You can use any combination depending on how you want it to sound, you will get the feeling for it naturally as you become better.

As you know, tetrachords are made of 3 tones (1, 3, 5), you obviously play 1 (root) with thumb and then with your other fingers you should hit each of the 3 and 5 at least one time. Depending on this you also get 6/4 and 6 chords.