I'm a pledge class of one, believe it or not. I'm the sole pledge in my chapter, and they weren't really looking for any. We just mutually agreed that I should join.
Anyway, your social ideas are great, though not everyone may like alcohol. If you do a Margarita night, you may want to offer an alternative to alcoholic 'ritas. Maybe a non-alc version for those who tee-total (like me).
My 2c, though that may not be worth much in today's market.