if it went wrong আপনি could seriously injure yourself because the belly button is dangerously close to several organs and blood vessels, its definitely unwise, though im one to talk, cuz i want to get my eyebrow pierced, though fully aware that the eyebrows are close to a major facial nerve.
Well they hurt depending on the ink, how well your skin takes it, etc. But I think a piercing would look really good on a flat stomach. If আপনি already have a flat stomach, people will become even আরো attracted to আপনি with a piercing there. Just make sure it doesn't get infected অথবা it will become crusty and disgusting.
The decision is entirely yours. I have a lot of piercings all over my body. Body modification in the form of piercings and ট্যাটু are a hobby for me, and every time i get a new one i feel better. If আপনি want to get your navel pierced, then do it. But i caution আপনি to keep it clean as infection is rife. And as it's near the centre of your body, any infection can go either way and cause major damage to organs, skin cells blood vessels etc. Also, make sure you're not allergic to anything the artist will be using, any metals the piercings will be made of, any latex gloves, liquids, medicated sprays etc. And if the slightest thing goes wrong, আপনি go straight to the hospital but DO NOT take it out! Taking out infected piercings, especially those in the naval/genital areas could cause আরো damage then good. Leave it to medical practitioners to take it out. But through all the bad things that can happen with any piercing/tattoo অথবা body modification at all these are very rare (make sure the artist is fully certified/qualified first). I have my naval pierced, and i have had no problems with mine :) As have my friends. The choice is yours.