I just finished a few quests at Bitter Springs including Boones sidequest and I'm rather curious about all this... Will I be able to repair the relationship between The Great Kahns and NCR? After Bitter Springs it seems highly unlikely but I want to make as many allies as I can for the NCR for the end of the game. Also, once I killed the Great Kahn who was sniping people at Bitter Springs I become Vilified by them.. Did I just screw the chance to become allies with them?

Another small question, I have 5 Strength and the requirement for the Anti-Material Rifle is 6. Will there be a major problem with me using it? I havn't really noticed much of one but eh...

I could use some help here :/

If you killed the Khan at Bitter Springs (Climb Ev'ry Mountain quest?) and are now vilified by them you've probably burnt your bridges - it's inadvisable to kill faction members if your longterm plan is to take a more diplomatic route! I can't think of any way to improve your reputation with the Khans because they will probably shoot on sight now, even if wearing Khan armour you could get to their camp but speaking to a named NPC will cause them to see through your disguise and draw weapons.

As far as the strength requirement for weapons goes, if your strength is less you will get more sway when aiming so your accuracy is reduced. I managed to get most of the way through the game using a sniper rifle (strength required 6) with a strength of 5 without too much trouble though, it's not the end of the world.

AM rifle requires 8 STR, not 6. It's a weapon that the Weapons Handling perk was designed for. It's very usable with lower STR, but if you're at the appropriate level the scope is basically still while you're kneeling. Makes life much easier.

You can try talking to the Khans while disguised, but Epona may be right in that you're SOL in terms of actually conversing with quest-givers. You haven't lost a chance at more allies, though- the Khans will not help NCR. If you get Papa Khan to listen to you ("Oh My Papa", given by Regis), you can convince him to move the Khans out of Red Rock when the battle for Hoover Dam starts. This allows you to avoid killing off the Khans as ordered by Col. Moore in For The Republic Part 2.

Also, if you are able to talk to them and you want to feel a little better about helping a bunch of drug dealers, you can convince Jack and Diane to make more beneficial chems like stimpacks instead of just addictive ones like Jet and Psycho.