This uses Pathfinder's method of poison.
I'll fix it.2. As written, Plague of the Swarm creates a contagious disease, i.e. it can spread from the immediate target to others. Mere toxins should not have that effect, so you'd need to either change the rules (perhaps just have it do 1d6 damage to an ability score of the Living Hive's choice, and don't mention Contagion), or change the fluff to justify the rules.
Pathfinder has XP value with every creature's stats.3. Your entry for a One of Many says it's worth 200 XP, but in D&D the XP value of an enemy is dependent on its CR and your CR, so it can't be a static 200.
That comma is a typo.4. You said that the living nest template gains swarm attacks; what are the details of those? (Unless you meant that it gains immunity to swarm attacks, but then you should write "It gains immunity to poison and swarm attacks" with no comma, to avoid confusion.)