Welcome Lily!!!!
We may be able to help you out with some of your questions!

There are a lot of your sisters here who have "been there done that!"
As for bra sizes, there are two parts, one is the band size (length) and that is the measurement around the thickest part of your chest. GG's (genetic girls) take three measurements around their chest, top, middle and bottom, but "we" don't necessarily need to do that unless you are having a custom bra made! Say your chest is 40" then that would be the size in the bra. The second is the "cup size" that is, can I say, how much "boob" you want to express!

It is my considered opinion that you don't want your boobs arriving anywhere 5 minutes before you do! A common mistake that a lot of CD'ers make. Bigger is not necessarily better, so stick with a B - C or at most a D cup depending on your physical size.
You will usually see a tag inside the bra next to the hooks and in large print it will have something like 38B or 36A or 40D. The first number is the "band" length (your chest measurement) and the letter is the "cup" size.
The bigger person you are the better able you are to wear a C or D cup.
If you weigh 140 pounds and are 5'6" tall, for God sake don't wear DD or DDD's for reasons you will learn about later.
Virginia