Usually a week ( 7 days ) or longer (14 days), it is important that the swelling has settled, if not wait a bit longer. If the stud is too short it can damage the piercing if for some reason the piercing swells up again.
Your piercer can, but you should not attempt it as you could injure your new piercing and it could lead to infection.
All initial lip piercings have to have a titanium 1.2 x 10 mm stud ( it's about the size of a small pea) then after two weeks the piercer should change it to a smaller stud or gem depending on swelling and healing :D
When I got my lip pierced, they already had the jewelry with them, because they have to use a special, longer stud to accomodate swelling. Perhaps if you brought you're own ball(s), they would screw those onto the stud instead of the regular ones.
I have both my lip and belly button pierced. I had my belly button pierced with a hoop and my lip pierced with a bar/stud. The belly button was more irritating then the lip because a hoop piercing requires the piercer to clamp it shut and fiddle around with a new pierced part instead of just screwing a ball on. I recommend any new piercings to be with a bar/stud as it is quicker and less irritating. Put it this way, I'm going for a 2nd lip piercing and not another belly button piercing ;)
Yes, it is possible to get your lip pierced with an eighteen gauge stud, however, the size and style of the stud will ultimately depend on the piercing professional's recommendation and your anatomy. Make sure you consult with a professional piercer to determine the best size and type of jewelry for your lip piercing.
You can but it's not the wisest thing to do with a brand new piercing due to the possible hook factor.
You follow the needle threw with the stud.
The jewellery for piercings isn't something you buy off the shelf, the piercing needs to be measured and size according to what you were pierced with and where the piercing is at with the healing. You need to see a professional body piercer to get the appropriate jewellery for your piercing.
yeah you should be able to, as long as the lip ring is the same thickness as the stud you had your nose pierced with, otherwise the ring will not go through. :) hope this helped.
On your lip...
If the jewellery was clean you should be o.k.
Wait 4-6 weeks after getting a lip piercing to change the jewelry in it