[Summerglow]

How much cleavage should show that you know you got the right fit?

[AbiDrew85]

I believe that VS bra's are accurate in the band but about a half-size small in the cup, so if you fit a VS 32C perfectly you are about half way between a 32B and 32C.

That said, you are of course best served getting a bra that actually fits perfectly than trying to fit into a bra that's too big or too small. So at least until you grow into a "true" 32C I'd recommend continuing to use VS.

Amount of cleavage depends on your own size and shape and the style you're wearing... If you have boob hanging out and giving any strange shapes like quadraboob or anything you're not wearing the right bra size, and it's probably too small. If you're getting squishy cups that aren't being quite filled then you're wearing one that's too large...

The idea of the proper fit is that your breast completely fills but doesn't OVER fill the cups. And of course the band needs to be nice and tight.

[Cranberry]

I'm a little late in replying. I personally don't believe in the add 4 method, it's outdated,but I know a lot of ladies here prefer that. If you use the add no inches method you would be a 30D, a 30DD if the bra you measured with is unpadded. Try one on if you ever have the chance, I know they're rare but you might be very surprised at how much better it fits. D cup doesn't necessarily mean bigger, it's all relative to the band size. Also, I don't think that's flat chested at all! It's very proportionate!
This chart shows sister sizes you could wear, sizes in the same colour have the same cup volume, but a different shape. So a 30D is the same size as a 34B, but on a smaller frame.

Hope I could help!
(By the way, the CC measurements that aren't in bold are inaccurate.)

[Summerglow]

I got my VS bras in today. They both fit differently and one fits better than the other. The band size feels better as a 32. I think I probably fill them on the smaller end of the spectrum, especially right now without any luteal swelling. It's funny how the cups seem to fit better in a 32C than a 34B. Some day I will try on a 32 B also.