So, the National Electric Code doesn't say anything about the number of outlets on a breaker, but it does specify the number of wires allowed in a junction box, which seems to be your main question.
Since you have no drywall, we can assume that you are using "New work" boxes, but you should check their labeled size (in cubic inches - ci) to be sure of what you're working with. A typical "deep", new-work box is 22ci. If you are using 12/2 Romex and putting an outlet in the box, the required size is:
- 6 conductors coming into the box: 6 * 2.25 = 13.5ci
- Your outlet counts as 2 conductors: 2 * 2.25 = 4.5ci
- The ground wires count as one: 1 * 2.25 = 2.25ci
- Required size: 20.25ci
So, you should be fine. If you're using 14/2 (probably - I went with the worst case for the example), the multiplier is 2ci rather than 2.25ci.
Wiring it together
If you have one pair coming in a box and one going out, using the screws of the outlet isn't a hack, and they even sell nice "backwire" outlets that are made for that. In the box where you are "splitting off" and you have three pairs, a pigtail to the outlet is probably better than filling all the holes in a backwire outlet. (Note, the pigtails don't count for the cubic inch calculations)
Also, in your "junction box" all the wires need to be folded nicely and pushed to the back before installing the outlet. The outlet shouldn't be used to force the wires into the box - you should be able to push the outlet all the way in with no resistance from the bundle in the back.