Prototyped Procedures

What is the best way to perform Procedure prototyping 
I would like some rules 
I am not sure if I am performing any steps that are unecessary
This is in the caller
D/COPY MYLIB/QCPYSRC,GETGRP_PR  

This is what is copied in
D GetGroup        PR             1A   EXTPROC('GETGROUP')    
D  $Group                       10A                          
D  $Cust#                        8S 0 CONST OPTIONS(*OMIT)   
D  $Item#                       25A   OPTIONS(*NOPASS)    


Here is the call for the Procedure (um Function)
EVAL      $CustGrp=GETGROUP($Group:CUST#) 

Here is what is in the called Procedure
D/COPY MYLIB/QCPYSRC,GETGRP_PR                             
PGETGROUP         B                   EXPORT               
D GetGroup        PI             1A                        
D  $Group                       10A                        
D  $Cust#                        8S 0 CONST OPTIONS(*OMIT) 
D  $Item#                       25A   OPTIONS(*NOPASS)     
D  $Found         S              1A   INZ('N')             


Also what are the advantages to setting up multiple sub-procedures in a
single source member
What limitations does this have 



I am always doing things I can't do; that's how I get to do them.

 -Pablo Picasso