These are engineering questions. Espresso machines contain water and steam at high pressures and temperatures. Bolloxing any of these line items could seriously injure someone- probably yourself the first time you try to use the prototype. All of these questions can be answered with pretty simple calculations based on temperature, water volume required, etc. If you can’t do those calculations, consult someone who can. If you just want to copy a working design without making any substantive changes, then find a good machine, buy it, tear it apart, and copy it exactly, without changing anything you don’t understand.