Wow... I totally dont understand that drawing...lol To answer your question, yes what the plumber friend told you will be fine. Run a 3/4 trunk line for hot and cold and pull off 1/2 to feed each fixture. at end of line use 1/2 to feed last fixture. no worries.
Here's an easy rule of thumb 1/2 inch line feeds 1 or 2 fixtures 3/4 line feeds 3 or 4 or more.