Bookini is in English, US terms only.

Swimsuit yarn is best for this project as it will help with support and shape. Any other yarn will be best to use this as a prop or over the bra just for fun. This is cute and silly but, as with any crochet bralette, cannot take the place of a true bra. Yarn is innately not supportive.
Cotton yarn in weight #3 would be the next best option!
~150 yards in skin tone
~10 yards for nipple color
This project does work up pretty quickly and is super fun! There are a lot of customizations outside the basic shape and idea. String tie, halter, corset, and ways to get extra support.
Everyone fits in each clothing item differently, combined with everyone’s yarn and tension being different, so trying this on along the way is critical for success.