I stumbled upon Cottonwood Cove and all of the Legion soldiers there. I had no followers with me at the time, but do have Boone and Rex back at the Strip which I just went into. Not very far into the main quest.

Anyhow, the legion guys attack me on sight at Cottonwood. The ONLY dealings I've had with Legion are at Nipton when they tell me to spread the word about what they did there. Should they be hostile towards me?

*found my answer "Seeking out Cottonwood Cove on the Render Unto Caesar quest, while Craig Boone is your active companion will make everyone hostile to you, despite Boone not being visible (likely stuck at the Lucky 38)and the fact that you have Caesars mark."

And most importantly, do I need the Legion men at Cottonwood for the main quest or anything else important? I saved before I went in, and ended up killing all of them. I got some really good loot in the progress. But I'm afraid killing them all might be a game breaker.....although I did not get a popup message telling me so, or if I did, I missed it.

Also, I've heard the Sniper's Nest there has a good item....but did not see a Sniper's Nest anywhere near Cottonwood. I've searched the area high and low, found nothing. Where is that?

First of all i don′t think that you need the Cottonwood men for the main quest atleast i didn′t but i didn′t kill them either.

Secondly Fast travel to Cottonwood Cove and then look NW, there should be a little empty triangle on your compass under NW. That′s the Sniper′s Nest, just follow the triangle.

I'm debating to reload to before I killed them all, or keep going. I'm just worried about some huge negative connotations to killing them all.

there may just be a NCR quest to clear the place out. (not directly associated with the story)

Well, I played on. The only thing I've noticed so far is Legion assassins being sent after me. They aren't that tough....more XP. And I'm "hated" by Legion now.

There may or there is?

I was about to clear it out and im going to side with the NCR. Id rather wait to do it under a quest.