I just use the Arduino IDE tabs; The main *.ino contains all the defines, inits, setup and void loop(). Then any other tab can be named whatever I want and contain as little as one line or a whole group of voids and/or Blynk functions… I found that no particular order was needed, a call for a void or function just works, regardless of which tab (or the name of the tab) it is really in. So I simply arrange everything into groups that work for my cognitive understanding 
In the folder, they all appear as *.ino files bearing the names of the tabs, except of course, the primary file with the sketch name.
Based on what @Jamin’s project shows, there is apparently other ways of splitting a sketch… hmmm.