Re read the codex
The worded it weirdly but on purpose.
One Noise Marine Per ten models may replace his bolt gun with a blast master. As everything else is worded saying for every 5 or 10 models I would take this to mean even at 9 or less models one is able to take a BM an more as a limitation on not being able to take more then 1 for 10 or less models. Now I may be wrong and I don't play them often anyway but until FAQ or Errata fixes the wording we allow it where I play.
On a side note the list looks good except I hate ectoplasm Cannon