For a sniper, I recommend a strength of 6. This will let you use up to the Sniper Rifle. At level 16, you can get a perk that reduces strength requirements by 2, letting you use the Anti-Materiel Rifle.
Or you can save the perk slot, wear power armor and use an implant for it.
Str, Per, Agi, and End should all be at 6 or higher for any sniper-type build for specific perks and weapon requirements. Trigger discipline is also a necessity if you're planning on max-range sniping enemies.
Aside from that, unless you're min/maxing your build you can do whatever you want.
Trigger discipline only reduces spread by 20%. It's one of the worst traits for a sniper because rifles in general have very low spread, you don't even notice the difference unless you mod weapons so the range limit isn't there, in which case gravity plays a bigger role.
It doesn't even help in VATS all that much because it increases AP costs by 20%.
As far as traits and sniping go, Small Frame*, Fast Shot and Built to Destroy are the best. Built to destroy alone is 15% crit chance for the Sniper Rifle and Gobi Campaign Scout Rifle.
*Agility is only needed for perk requirements, which small frame helps with. The combat stat of choice is Luck.
[e] This, of course, is regarding a Guns sniper oriented build, where Trigger Discipline's 20% VATS accuracy bonus or Agility's reload/draw/run speed bonuses are not much of a factor.