Betweeen 4 and 6 mm. The most common is probably 5 mm.
14 gauge is bigger, the lower the gauge size, the bigger it is
Each barbell is scaled to the size of the tongue to be pierced therefore there is no "actual size" barbell for tongues, this is why you need to have the piercing done by a professional body piercer who will scale and measure the tongue and place the correctly sized barbell into the piercing.
Very carefully, depending on the size of the swelling.
The barbell used is scaled to the tongue being pierced to ensure there is room for swelling and discharge. The professional body piercer will ensure that the right size bar is used and every tongue is different, there is no specific size (only a ball park guess nothing more). To find out how long your current jewellery is would involve you removing the barbell and measuring it with a ruler to know what size is in the piercing right now. If you do this be sure to use care in handling the jewellery and ensure the piercing is not contaminated by inserting dirty jewellery into the piercing.
For a standard nostril piercing, 18 g.
Generally a 14 gauge barbell, this may differ depending on preference.
There is no tongue size requirement for a tongue piercing. If you want your tongue WEBBING pierced, you have to have a certain type of anatomy (i.e. have to have a webbing that's there all the time, even when your tongue is at rest), but just a regular tongue piercing is possible on everyone. Your piercer will tell you your best/safest options for PLACEMENT (so you might not get it precisely where you wanted it on your tongue), but, as far as I know, everyone can get it done. Unless maybe you have overly huge veins and it was just too risky, but I'm just speculating there.
It's not recommended to pierce your tongue yourself as it can lead to complications like excessive bleeding, infection, or nerve damage. It's best to go to a professional piercer who will have the proper tools and expertise to safely perform the piercing. Typically, a 14 gauge needle is used to pierce the tongue for a standard tongue piercing.
I am guessing this is a serious question, so if you keep your mouth shut no one will notice a tongue piercing and if you don't chew gum like a cow or laugh open mouthed you should be fine. Being an oral piercing they are not noticeable at all unless you draw attention to it, that's why I couldn't believe this was a legit question, so there you go.
Of course you can, the only difference from someone with a longer tongue is that the piercing would have to be a bit closer to the end of your tongue. Other then that it doesn't change anything.
That is based on the tongue size ( not all tongues are created equally ) the thicker the tongue the longer the barbell. This is to make room for swelling. Your professional body piercer will check your tongue and size you for the right barbell to do the job. Two weeks after the piercing is done the swelling will have eased off and a shorter barbell can be put into the piercing to avoid doing dental damage.
Either 16ga or 14ga