I do not have a pattern made for the breastplate that can be printed out but the video is a tutorial on how to make it as it is based off of whatever pattern you are using for the leotard itself, thus it is quite versatile
That's an option too that I have considered, but my leotard is relatively easy to slip out of, so using the bathroom wasn't an issue... and I guess I am just used to having to go to the bathroom in leotards from Figure Skating and...giant hoop skirts for skating lol
Senshi costumes are quite difficult so I praise you that this is your first one!
I went through three leotards trying to perfect one :/ One was for Sailor Cosmos, one for Neptune and another for Moon >.< I had used the Green Pepper pattern by itself then tried to follow Cupcake Cosplay's (but their tutorial wasn't very clear and seemed to lack important information and it just didn't work out for me). So I had to try a different approach
For the leotard always use a 4-way stretch. The pattern I used is not meant for a non-stretch material as this leotard is one that you step into, there is no zipper. For the skirt, bows, etc. You can use whatever you'd like. Keep in mind though if you use a stretch material for the skirt, you cannot get solid pleats but more like mine where it is flowy. If you want solid pleats, you'd want to use satin (preferably).