You want the stomatopod's legs to touch both sides of the burrow and be able to do a 360 if it wanted to effortlessly. See the animal in person first before buying the pvc (too late..)
Like gary said, you don't want the burrow to be stagnant.. and unforunantly in smaller burrows for smaller stomatopods you can't fit a small pump so all that complicated structure is asking for disaster later on.
Plus when stomatopods molt they need to close their burrows.. if most stomatopods have trouble handling 1-3 cavity openings naturally.. imagine 5 in a maze like structure. N. wennerae actually closes their burrow EVERY NIGHT. Mine is closed up til morning right now!
Also I heard roy likes to sand paper the ink off of the pvc. I do so myself.. sand paper the ink, any sharp cut edges, etc. It's low risk not to so no worries but it's a precaution.
This isn't my vid but this is how tight they love to fit in their homes.
<iframe width="560" height="315" src="//www.youtube.com/embed/55ujSZSsTns" frameborder="0" allowfullscreen></iframe>
You're really cutting it close with the pvc.. and you don't even have the animal to size it yet!