I have my nostril and septum done. I wear a screw in my nostril ("stud") and a crescent/tusk in my septum (open ended ring basically).
How long was it red/swollen?
Couple of days, if that. it didn't really hurt all that much.
What if I get a cold?
it's no big deal.
Anyone have issues with infection?
no, but know your piercer and his/her procedures. also don't over clean. in fact, some piercers recommend not cleaning at all. i didn't have any special cleaning to do with either nose piercing, and they healed up quickly. if you are a normally groomed, clean person, it should be the same. :D i assume you are.
I am very metal sensitive, would you recc stainless steel or 18k gold?
i recommend titanium. titanium is the most bio-compatible metal. if you are going with steel, it would be surgical grade steel, which should be fine for most people. I do not recommend gold, as most of the jewelry made for body-jewelry/piercing use is made by specialists who focus on titanium, niobium, and surgical steel. Some companies will have gold lines, but it's pretty uncommon, and the gold jewelry that is not made by these companies tends to be low quality in some way. this is just my experience, though.
you want to look at companies like anatometal who also have gold lines, but titanium works well for people with metal sensitivities. and it works much better than gold. it can be difficult to find titanium nostril screws, but they do exist. they are also more expensive. but, since you wear it all the time, it's really worth it.
i own three screws and three crescents; i tend to wear one for months and months before switching it out.
If you remove it in the future, how much does the hole close up, or does it look like a big blackhead (eww)?
most retired piercings just look like a small dot, if that.