How do you define the size of a rectangle, circle or node in TikZ to be scalable, like when you position objects using
(1, 2) and then apply
scale=2? What I'm looking for is to be able to scale the objects like circles and boxes along with the coordinates.
You should do your diagram as at the scale you think you want, and then if you want to scale the figur, say to half its size, apply
The blue is the original with a default
If you want to scale the text as well you should have a look at How to scale Tikz drawings and text together?