Not sure why'd you want to loot a centaur, but that's why the Remnants killed you;
you tried to loot a dead corpse during combat, even if it didn't have anything in it, and that makes them be hostile.
And for good reason so that people can't just go around looting every Vs. encounter they get (though it is very ineffective in big encounters, since you can just loot the corpses after combat ends).
A good starting city would be Vault City, much less people than NCR. Chances are you won't get randomly bursted or encounter another player every 5 minutes. And since you love looting at battles, there are lots of good "Vault City Patrol vs Ghoul Crazies/Strong Slavers" so that you can get a loot (wait after the battle ends, of course). Just make sure you stay far away from the ghouls because they are good sharpshooters.

And there are tons of brahmins near Modoc, so you can get your 10 hides, then make a tent near VC.
Try getting a gun from the Ghouls, and then kill brahmins in
real-time because they move a little bit slower than you, so you can charge your AP, shoot, run, charge AP... kill brahmin.