Infections, side effects and healing issues are all points you need to discuss with your professional body piercer BEFORE you get the piercing done. You also need to discuss aftercare for the piercing, this should be followed up with written aftercare instructions for your piercing. No professional body piercer will force you to purchase aftercare products, this is a purchase that is up to you and they can only recommend specific products but they can force you to buy what they have.
Listen to what you are told and follow the aftercare to the letter and remember if you are having issues with bumps and lumps or discharge go back to the shop that did the piercing and talk to the piercer. They must help you resolve any healing issues you may be having. Don't solicit advice from anyone who is not a professional body piercer, just because one thing worked for someone else doesn't mean it will work for you. Healing issues need to be looked at first hand so the problem can be recognised and resolved, the internet is just a guessing game.
I would not recommend riding a roller coaster. The force of a roller coaster is almost the same as the one that astronauts experience on a rocket. Plus you will probably squish your belly in the safety seat or you may not be able to pull it down far enough to be safe. A merry-go-round or a Ferris wheel are safe to ride on.
stitches...
Yep. Most jewelry isn't magnetic if thats what you're worried about. Some coasters have restraints that could hit or rub against the piercing so that might irritate it but other than that, you'll be fine :)
I would check back with your doctor; the stitches may not be dissolving properly and will have to be removed.
No.
Your belly button piercing hurts more then a normal ear piercing your belly button piercing is more sensitive then a ear. :]
getting hit in the belly or falling and landing with the belly on something rounded.
not possible
Yes you can
Sometimes when the vet has spayed the dog they can often end the stitching (a knot) leaving a piece of the stitch too long that can dig into the dog's belly. Either you can cut off the extra or take the dog back to the vet (there should be no additional cost for this) and have them check the stitches out. Stitches don't stick to the skin, but are sewn in. The vet would have told you when to bring the dog back to have the stitches removed. If the wound looks good and the dog is irritated by the stitches (each dog, just like a human can heal quickly or slowly) perhaps it's time for the dog to have the stitches out. See your vet right away!
When you get your belly pierced its doesnt hurt at all. its hurts as much as a little pinch.
No time. Getting your belly button peirced is very dangerous. You can get all kinds of infections.