You want to break down the design from your idea to ‘parts’ that make the vest. This will be based on dimensions (child, adult, etc) and maybe style.
These vests are made of inside and outside cloth, floating element (which has a thickness), and the various attaching straps. Since you already know how cloths will be cut and bent this should be for you to translate into Rhyno - but you need to learn the tool (how to draw in 3D).
But it’s basically make the seams and ‘loft’… Then add thickness. Layer the 3 elements per vest element (the back would be the easiest to start with i suppose).
After that i would go watch how to model (and set dimensions).
Here is an advanced video for modeling something organic (and shirt-like if you abstract from the airplane shape).