When we get around to the Noble, does the "Hit Dice: 58" mean they are actually meant to have "fifty eight" Hit Dice, or is it a missing hyphen typo and the original was intended to be "five to eight" Hit Dice?
What am I thinking, the THAC0: 3* answers that question. If it had 5-8 Hit Dice it'd have THAC0 15 or 13, so they really do have 58 HD.
It just seemed an odd number of Hit Dice for them to have. Why not something more even like 50 or 56?
Well, sticking to the standard one, I'll go for Diminutive also. I'd set the Dex to 10 probably, along with Wis 10. The extraordinary reach is good. I'd probably remove the "shoal" option from the organization, since that's what the swarm's for.
You know, mathematically speaking, 58 HD is just as even as 50 or 56.
I'm just not very fond of an organization of up to 200 as a shoal. I know that the swarm is many more critters than that, but I think the intent was that a shoal is "that's too many to be bothered with counting," that that's the function of a swarm. It's just not reasonable to expect a combat or other interaction with 200 individuals. While the numbers wouldn't match up with the original, I think it's better to follow the intent of the original monster rather than the hard number.
I notice I forgot to reply to the Dex issue --- based on your logic, low Dex is ok.
I'm ok for that organization as long as we note somewhere in the flavor text that a gossamer swarm is also sometimes known as a shoal.
Starborn like the gammaroid should work.
The poison is a "nauseating paralytic poison. A saving throw versus poison offsets the allergic reaction." But that doesn't let them kill anything with the poison --- though I guess a paralyzed victim may get killed by many 1hp stings. Anyway, I wouldn't mind adding some Con damage too. What do you think?