Fountain seems like it would be playable at first glance but scenarios like having a sister and a pridemate in your opening slows us down a turn and doesn't immediately help him grow. I think with a deck that has problems with interacting with other decks, having a sister in play T1 is more important.
Hey guys! What about ajani's welcome? It's a one-sided sister but it's an enchantment...so it's bit less vulnerable to removals. What do you think?
One-sided Sisters usually don't trigger enough to be relevant. The fact that it won't trigger other sisters on casts also hurts it. Probably not worth running.
As for Isolate, it's a neatly designed card. Getting rid of Vial slows down a ton of decks - it also kills Cranial Plating while giving us a way to kill a turn 1 Bird or Noble. Probably worth a look for the sideboard.