I want to make this for 12 people. Should I triple the recipe? Also should I use baby spinach?

Baby spinach is going to shrink more than "grown up" spinach, so tripling is probably a good idea (I am a fan of better too much than not enough) I think you will need to play with the cream and milk amounts, depending on how much the spinach shrinks ... this looks like good leftovers so I say go for overdoing it and eat the remaining with a poached egg in the morning!!!