Try to think about how much mana you have available each round and how you're spending it. It takes a full action and 12 mana to summon Felella. After that she can only cast one enchantment each round, and your mage can only cast one enchantment each round. With your full action being used to summon a creature each round and your quick cast and Fellelas action being used to enchant the creatures you summon, your strategy is going to get predictable very fast and you will be too inflexible to respond to threats, and you certainly won't have enough mana to swarm.
My advice is that instead of powering up your swarm individually with enchantments, try using zone conjurations with arena wide effects. I'm actually currently working on a Beastmaster build that uses Rajan's Fury. Low level animal creatures, especially those at level 1 are what you need most for a beastmaster swarm. The beastmaster can summon a level 1 animal as a quickcast, which means he can summon up to two animals per round. Add in a lair and that makes three animals per round. Of course, it might be more effective to try summoning a bigger creature in the beginning to distract your opponent while you setup your swarm, rather than using a lair.
Another thing you could try is a few big strategy. Try summoning one or two more powerful creatures and buffing them with enchantments. Fellela can be useful here. If you plan to move your mage around a lot to help support a semi-toolbox few big strategy, you might like Animal Kinship, since that buffs your mage just from the types of animals you have out in the arena.
