I love pirahnas for ELO, and I think you have the right idea with this fairly budget dack.
I think the key is to keep your draws consistant and varied. You want your opponent to have to account for every card from 2* to 5*. Thats why the Hawkins cards work so well.
With that in mind I ditched Puff from my mono deck because he doesn't do enought damage and his 9 power isn't enough to make him a true wall card. I would also look passed Sliman. Remember that if its a draw in a match the card with the lower star value wins. That means you always need one more pill with Sliman. Also, he is realy vulnerable to attack manipulation cards (like the excellent Talijon).
I like the idea of playing with Kristin a bit to see if she suits your style. Other than that I'd save my clintz for some Pirahana's staples like Tula who it sounds like you will be able to afford soon enough.