The mods as well as the enhancement are tricky, but the thing that you want to look out for is the mods with A and B in their name, you don't want these in your gear at all, the either got high mainstat, for you cunning, and lower power, or low cunning and high endurance. You want the ones with 56 Cunning/34 Endurance/44 Power, numbers are for Hazmat/Dread Guard or Crit, 53 Cunning/32 Endurance/41 Power or Crit, numbers are for Black Hole/Campaign.
Stats for snipers is slightly different depending on specc, but lets say that 300 crit raiting, 300 surge, 300 accuracy is a good start, from that point only focus on power. Crystals are very cheap on the GTN, you won't get your favorite color but that don't matter to be honest, Here is my gear/build for Full Lethality Specc
and Here is my build/gear for Hybrid Specc
, be aware that I have full BiS gear so you should focus on getting the same gear, but the number 26 (instead of 27 that is BiS).
No worries if you don't have Cybertech or Artifce, just that you can get a lot of cash that way by RE:ing gear, something to think about if you are creating an alt and pick a new crew skill. Yes, the relics is good and doing dailies gives you money as well as gets you closer to them, as a Sniper, you want one DG of Dark Radiance and one DG of Boundless Age. Also correct on the mainhand thingy, the PvP ones are good but you should take any chance you get to get a Campaign one, or just put in the mods and stuff from the Black Hole gear you buy and keep the PvP Barrel for right now.