Limited slip will transfer an (obviously) limited amount of power to the wheel with greater resistance in the event that one wheel begins to slip. Conventional ('open') diffs transfer all the power to the wheel of least resistance (and therfore lowest traction). The opinions on LSDs tend to differ... but I mostly hear of people saying they aren't worth it.
Gear ratios will affect most noticably your power, rpms, and gas milage. Lower (numeric) ratios, such as those in the 3's, will have less power to the wheels, but on the highway their rpms will be noticably lower than those of us with high (numeric) gears... those in the 4's (4.10s... etc). A higher gear number will provide lots of low-end power (torque?), you'll jump off the line faster than a ricer, and pull stumps like there is no tomorrow... but you'll pay when you hit the highway, burning extra gas and revving a bit more. Obviously this is over-glamourized, you can still pull stumps if you dont have 4.10s... it's only going to be somewhat harder.
I hope this helps a little bit... my knowledge is limited on this
-----Nate