Yeah, so first you're going to want to go on Ewa's website and click the union flag at the top of the page. That will turn it to the English language version of the site, and will show bra sizes with their UK conversions.
With the search box at the side (with 4 drop-downs and a type in search filed), you will need to select all the things before pressing search. For some reason, if you select your size, then press search, then try and select a style and press search again, it doesn't work.
I've just yesterday explained to Ewa via her facebook page that about half of the custom lists had 28s and above listed, but no 30 bands. This being said, often searching by size isn't particularly helpful because with a lot of the bras, your size won't be in the drop down menu, but she will be able to make it for you anyway, even if it's not a custom size.
Once you add something to your basket, and click to pay, you'll need to press payment in advance. I then get transferred to my paypal, and then complete the transaction. I get an email straight away but the money always takes a few days to come out. It usually takes up to 3 weeks for them to make the bra for you (unless you've found your size in the "48 hours" section of bras that have already been made)
I've bought nearly 25 bras in the past year from there, so am happy to answer any other questions /u/scisess