I don't believe that Gears of War 3 pays attention to what body part is being shot. A shot to the head obviously does more damage with certain weapons like you said. Getting shot in the arm, leg, or chest should do the same damage with most weapons.
Besides the head, GoW 3 doesn't have specific damage modifiers to certain body parts.
On a side note, when I was searching for a chart for proof of this, I found a chart of the weapons and their damage, fire rates, and clip size. This could be useful in some way to you:
http://www.ign.com/wikis/gears-of-war-3/Weapon_Statistics_Chart
From experience, a single command post is sufficient to occupy the money and man-power of two players. Unless you want to spread out or, as Tom-grochowicz mentions in his answer, build a back-up base, there isn't a lot of gain to be had from building this in the early game.
However, if you are playing with more than two people then the additional defences unlocked by having a second command post can be used to compliment each other. For example, you might want a turret per person, which you will need at least another command post for.
When you haven't been playing Horde mode long, there are certain unlocks for Horde 2.0 that a second command post can help with:
The Infinite Ammo mutator for Horde requires you to Earn a Combat Engineer ribbon 100 times
. To earn this ribbon, you must work on five fortifications in a single round [source]. A second (or more) command post will provide a new set of potentially cheap barriers to build and repair, which will enable you (and others) to get this medal faster. This will also help to level up your fortifications faster.
When you have been playing horde mode for a while, you will have achieved some or all of the fortification levels and unlocks. Many of these make fortifications cheaper to repair and maintain, which means you will find yourself with more money as you progress. You may find that you simply have a cash excess that you would like to sink into more barriers and decoys.
For example, with barriers, repair becomes cheaper at each even level:
- Level 2 - Spike Barrier Repair Cost 8% Less - Level 1 Decoy Unlocked
- Level 4 - Razor Wire Repair Cost 8% Less - Level 1 Turret Unlocked.
- Level 6 - Electrified Barrier Repair Cost 8% Less Level 8 - Laser
- Barrier Repair Cost 8% Less
Best Answer
Active reloading allows you to reload the gun faster than normal. This is achieved by tapping to reload and the tapping reload again when the reload tracker is anywhere within a grey bar highlighted on the reload gauge.
A "perfect" active reload is achieved when you tap the reload button within a much narrower white bar on the reload gauge. This fills the empty rounds in your click with special shots, indicated by flashing ammo symbols (for guns with bullets). The damage per shot is also increased by around 8%. (Except for the Scorcher).
These special shots have differing effects for some guns (paraphrased from above link):
As wilerson noted in the comments, if you click reload anywhere outside of the white or grey bar, before the reload is complete, then you achieve a "failed" reload. This confers no bonuses and increases the time it takes to reload the gun, such that it would have been faster to do nothing after starting the reload.
To summarise: Any active reload will cut down reload times. A perfect reload will grant bonus damage and some extra effects depending on the type of gun. A failed reload will increase reload times.