Hi Anan,
It's been good to hear of you again, pal!
De Gheyn's
Wapenhandelinghe was the first exercise manual of its kind, mainly regarding firearms, and consequently had many followers (the first of them being Wallhausen in 1616) which mostly confined themselves to copy the original at large, and on a lesser level.
Actually the volume the frontispiece of which is engraved 1607 but was printed in 1608, comprises three sections of weapon handling commands respectively: for the caliverman (45 plates), the musketeer (42 plates), and the pikeman (32 plates). There is very little text, just a summary of the single commands prior to each section. If you are especially interested in the text in Old Dutch I can scan and post it.
Generally you will be well advised to watch out and seek the web for the perfect reprint:
Jacob de Gheyn:
The Exercise of Armes (sic!), Lochem and McGraw Hill, Inc., ISBN 90-6087-271-1 or 07-016237-9.
I just noticed Amazon offering a paperback version at 14 USD:
http://www.amazon.com/Exercise-Armes.../dp/0486404420
As to your second question: in Germany, barrels with an octagonal breech changing to a round and longer forward section have been made starting as early as the late 15th century. The raised and acanthus leaves chiseled intermitting bands pictured by de Gheyn only arose in the 1550's. Actually not one single existing matchlock musket is known to be equipped with them ...
Best,
Michael