Does this game have blueprints like in SP?

Do you mean something like this?

https://www.simplerockets.com/Mods/View/71628/Designer-Tools

Nope. The designer UI is a lot more smooth and easier to use though. Also rockets are much more simpler and are more big tubes filled with fuel rather than a aerodynamic rocket. So looking up the dimensions for specific rocket parts is good enough

there's probably a mod for it somewhere, but there isn't any in the stock game