The following link also may help:http://www.dhammaweb.net/books/Dr_Walpo ... Taught.pdf
Page 32 states:
It should not be thought that the eight categories or divisions of the Path
should be followed and practiced one after the other in the numerical order. But they are to be developed more or less simultaneously, as
far as possible according to the capacity of each individual. They are all linked
together and each helps the cultivation of the others.