Always grease the face of the barrel nut that contacts the barrel. You do not want to torque the steel barrel alignment pin against the aluminum upper. This is especially important for some proprietary nuts for certain free floated tubes.
If you are even modest mechanically inclined ARs are super easy to work on. The only "special" tool you really need is an armourers wrench, the others make it slightly easier or a lot faster if you are building them for a living. Watch some free videos if you are still worried buy a DVD and watch it until you have memorized it then just start in. If you have a question just ask there are lots of people with lots of knowledge about ARs.
