I’m part of a group on Facebook called “Origami Kids” (the group is open so anyone can view it) where people post their creations and/or tutorials on a regular basis. Quite a while ago, I came across a post about a rosebud and calyx tutorial (the tutorial creator and the person who designed the model can be found following this link) which teaches how to make a single unit, as well as how to stick units together.
I had to spend most of my time cutting the sizes of squares required before I could make a start. The tutorial is super easy to follow, making units will be no problem!
Assembly is by sticking sides of calyxes together. The tutorial does suggest using 14 units total, but I couldn’t make the model work like that. Instead, I improvised and made a kusudama using 12. Stringing it up is fairly easy too.