My own comments, I'm afraid my knowledge is a bit more scholarly than practical. Hungarian gun laws are a bit strict and there is just not that much of a cultural interest in it as in America.
1. Gangsta style shooting is a perfect way to shoot and does not hurt your accuracy at all.
The sights are on the top of the slide for a reason.
Handguns are actually pretty inaccurate when compared to rifles. It is much harder to archive stability than with a rifle and the barrel is shorter.
2. Shooting in the leg's, arms or the gun itself automatically disarms and stops an attacker.
The problem with this, is that sometimes having a shot just scorching the ear of the the attacker is enough to make them think twice while other people were still fighting with a
bullet in their heart.
Terminal ballistics are a tricky thing but the underline is this: unless the bullet damages the central nervous system (ie, the spine or brain) no shot will gurantee instant death/disablement. Everything else is open to a variety of factors: where the bullet hits, what type of bullet is it, what angle, etc.
Shooting joints will do a good way to make the attached limb crippled (even for life) but will not gurantee that the attacker will stop moving. In general, "shooting to disable" is something I believe is best left to marksmen who know what they're doing. Sometimes it can work, but in a gunfight or close-quarters fight, there is simply no time to make such precise shots.
As for shooting the gun itself, I can't tell you what could happen. You might get nothing except a dent, you might make the gun cock-off, you might render the weapon inoperable or dangerous to use, you might even make the weapon explode.
Trick shoots like these I believe are best left to marksmen and even then only if the alternative is lethal force.
3. That firing in a one handed manner using a handgun grants you no accuracy loss.
No. You can fire a handgun with one hand with pretty good accuracy, but that's more useful for sports than for combat.
4. That gun recoil can knock you back, over or hurt you and impede on your shooting.
The shock of the recoil might, but the recoil itself not much so, unless you're firing a very, very, very powerful gun. You can get used to the very powerful recoil.
Except for some automatic weapons though, where the gun can become uncontrollable.
Edit: this is still true for the video: it was the gun being frightened that he practically threw away the rifle and lost his balance. If he made more effort to secure it, he might have not lost his balance. Also, the rifle in question is an "elephant gun", so it applies for "very, very, very powerful gun".
5. That shotgun's always have a large spread.
Untrue. What's interesting about shotguns is that they accept a wide variety of ammunition, some even pretty crazy or exotic. This is due to the smootbore barrels versus rifled barrels. Rifled barrels make the bullet spin and thus be more stable in its flight path, while smooth bore are a bit more like a canon, able to shot anything that can go trough its barrel.
As for spread, that only applies to buckshot and even that isn't very severe. There are various types of buckshot, which varies the balls size. Spread also depends on the length of the barrel. Speard can be pretty wide but not always.
6. That rapid shock and blood loss can quickly take over you. On top of that, putting a bandage on a bullet wound wont make it A-OK automatically.
This might be true, if you mean "quickly" as in minutes, then yeah, probably. I don't know much about the medical effects of a bullet-wound.
7. That bullets don't automatically fly cleanly through you.
Depends on the bullet, but true. Some will. Quite by itself, quite automatically leaving a nasty exit wound

.
A lot of things can happen with the bullet as it passes trough the body. Again, terminal ballistics are a bit iffy subject.
Some bullets, like the 5.56 NATO, can tumble in your body, diverting its path. It can also fragment once inside, making little bits spread out.
Hollowpoints and soft-points will try to spread out as it meets resistence. This has two effects: one is that the bullet will loss energy more quickly and penetrate less, two it will expand and create large wound channel. When it comes to hollowpoints is when body armour really makes a difference for the better (from the wearer's standpoint anyway).
8. That low caliber weapons can still be pretty deadly.
True, especially at closer ranges. A .22LR can still kill, although it can take longer.
9. That bullet impact does not blast you back 5 feet.
True, the energy recieved is roughly as much as was the recoil. Any thumbling or moving backwards is due to shock or simple unbalance.
10. That Sniper rifles are like gaming ones.
I would dare call this true, as you can easily have a perfeclty functional sniper rifle from a good hunting rifle and vice versa (as long as we are talking about rifles for hunting medium to large game). Several popular civilian rifles are modified military rifles.
In essence, any rifle with a scope and a strong enough bullet (that can take down large game) can easily double as a sniper rifle.
That said, military versions tend to have standarised railings (a picatinny rail, but some civil rifles has those two and addons for those can be brought by civs) and much larger magazine capacity. Militaries also prefer semi-automatics over bolt-action but this varies among various militaries. Also, there is a bit of a difference between civilian and military bullets: military bullets are more designed to penetrate (as body armor has come around in today's army) while civilian bullets can be various types of hollowspoints/softpoints (as animals seldom wear body armour, so you aim to create as big a wound channel you can to take the animal down sooner).