Erm ok, well some pills can change the size of your breasts but not massively. They might get bigger, might get a bit smaller, but it's not all that noticeable.
For how long you can wait depends on the type of pill you have. For mine, it's about 2 weeks and it says if you get sick use a condom for 2 weeks afterwards just in case. Have you spoken to your doc about your pills? They should be able to tell you exactly how long you should wait, or, failing that, read the leaflet in the pack. It will tell you there exactly how long you should wait before having sex without a condom.

For most pills:

If you start the pill on the first day of your period, you are immediately protected. If you start any other time, you should wait a week before having unprotected sex.

i went up two cup sizes when i went on the pill. but it really depends on the individual. yours may not change at all.

what eiri said is generally true about the pill, but make sure to read the instructions carefully to check it applies to your brand of pill.