Wearing a bra will actually feel BETTER - you may even want to sleep with it on. Sport bras provide the most comfort. The main important thing to remember is, if you are wearing a bra, don't allow moisture to build up. If you sweat, you'll want to change your bra frequently and cleanse your piercing before donning a new bra.
You will not need to change the size of your bra. The little ring isn't going to make that much difference and a snug bra will feel better during the healing process.
If your piercing leaks a little fluid during the healing process, this is normal. If you don't want this fluid getting on your bra, you can buy nipple pads designed for breast feeding mothers. These pads are soft and disposable, and can create a barrier between your nipple and your bra.
If you have heard about nipples staying hard (erect) once getting them pierced, that is not necessarily true. They may for a while, but once your body gets used to the piercing, your nipples will relax like normal. If you have flat nipples, piercing them can help to push them out a little bit, but that doesn't mean they will always stand erect.
If you plan to have a child and breastfeed in the future, you may wonder if you should get your nipples pierced at all. I've had people tell me they've heard all kinds of crazy rumors about breastfeeding with pierced nipples, but you only need to concern yourself with the facts. The facts are that in most cases, pierced nipples do not cause a problem when breastfeeding; in fact, some have found that it actually increases their milk flow (flow, not production), making it easier to nurse. Some nursing mothers say they even keep the jewelry in (including during feedings), although I personally do not recommend this. You need to carefully consider what goes into your child's mouth at all times, and a piercing can be a breeding ground for bacteria. It's much easier to keep it clean without the jewelry in place.
If you remove the jewelry permanently while you are nursing, the hole may very well close up and then you would need to repierce your nipple when you are ready. If you remove the jewelry only for feeding sessions, it shouldn't be a problem replacing it after the feeding is over. But constant removal and replacement of the jewelry can be annoying or even cause the piercing to become sore. Since breastfeeding can already cause sore nipples, you really won't want to cause any additional aggravation.
The decision is ultimately yours. You have to decide whether you want the piercing enough now, even if you may lose it later. Once you have a child, you will also have to decide if you are going to keep the jewelry in or remove it. Whatever decisions you make, it should be in the best interest of any future or present child. Nurturing your child through breastfeeding is one of the most important things you can do during the beginning of their life. Making sure that everything that enters their mouths and bodies during that time is clean and safe is also your responsibility.
So, unless you have a medical reason, getting your nipples pierced now and breastfeeding somewhere down the line should cause no complications. However, if you are currently pregnant or nursing, you will not be able to get any piercings until 6 weeks after the baby has been weaned.
Sensitivity & Arousal
Does having your nipples pierced make them more sensitive? Most women say yes! Does this mean you have to worry about walking around being aroused all the time? No. Especially once you get used to them, they will provide the most sensation when you want them to. If you're doing normal daily activities, you're not going to be walking around in a constant state of frustration!
Oh, and one more thing - tell your partner it's hands and mouth off for 2 weeks! Even if the piercing feels OK, it's not healed. Germs and bacteria can cause a painful infection, so you'll just have to find other ways to entertain yourselves. ;)
If your jewelry falls out or comes out involuntarily, you need to see your piercer as quickly as possible to have it put back in. Nipple piercings, even healed ones, can close very quickly. However, if you try to put the jewelry back in yourself, it may feel like it's completely closed when it's not. Your piercer can use tapers and lubricant to ease the piercing back open without having to repierce - IF you get there fast enough (within 24 hours).
Once it has closed partially or fully, you're looking at a repiercing. Can it be done? Of course. Will it be hard to pierce through old scar tissue? A professional and experienced piercer will not pierce through scar tissue if it is avoidable - they will create a new hole through soft flesh. Your nipples will be at no more risk to cause difficulty with breastfeeding with second holes than they would with a single piercing.