Weaponcraft Enthusiast 6 Three bodies in one card for a mere three mana equates to a pretty efficient all round deal
Building Soundwave, Sonic Spy as your Commander can be done, it just needs a strong focus on token Creatures, forsaking the midrange and control aspects that white, blue and black decks are well known for
You can have more, but I recommend sticking as close to 40 cards as possible while aiming for a ratio of 24 playable cards to 16 lands, adjusting for your curve as you see fit
It makes sure your deck is consistent and complete, helping identify what your deck might currently be lacking, letting you refine your deck lists independent of playtesting
It exiles your team and brings them back with an extra loyalty or +1/+1 counter
If the target creature is an illegal target as Eriette's Lullaby tries to resolve, it won't resolve and none of its effects will happen