I'm going to start a new playthrough, playing using only NCR equipment, completing quests in a way favoring the NCR, attacking its enemies and finishing the NCR way. I'm going to pick Guns and Repair, but I'm in doubt about the last one.I'm thinking about Barter. Any suggestion about that?

The traits I'm taking are Trigger Finger and Good Natured, and the equipment will most likely be 9mm pistol in the start(levels 0-10), Service Rifle later(11-20), finishing with Marksman Carbines and Sniper Rifles(21-30), all modded when possible. Respectively, I'm going to use basic NCR trooper armour, NCR Ranger and the Black Armour.
I'm avoiding to use food for healing, trying to use only Stimpaks and medication of the likes.
Any tips for playing like this? Some unique gun that is a must-have with this loadout?
Oh, and I'm playing on hardcoe.

Any perks that I need to have? What SPECIALs should I take?

Don't waste points on Barter, it's already too easy to make a ton of caps in the game. I'd recommend Speech myself, as there are a number of quests that can't even start unless your skill is high enough, and there's also a number that are much easier to finish with a high enough Speech skill. Repair is also kind of a waste in this game since you are always able to repair something to 100% regardless of your skill level. The only thing that Repair does for you is unlock a few crafting options. I'd recommend you go for Medicine instead. There's certainly a benefit in getting more out of your Stimpaks early on.

Survival fits the trooper role more than anything else. At basic training, they teach you to use your weapon, maintain your weapon, and survive in the field: