RE: what do i need to get my slow stick in the air?
Your SS will work fine with the HS 81's and the 555. With these electrics, you always want to keep them as light as possible, but the SS will carry a bit of weight well.
The packs Twmoody suggested are great: I get 22 minutes off a 7 cell KAN 1050 mah pack.
I have also flown with smaller 7 cell 650 mah packs and got less time from them: around 12 minutes.
The plane flys a bit more 'solidly' with the heavier packs. You don't want to go too heavy though--the 1050's are as big as I'd go. Cheap Battery Packs is a good place to get packs .
The Slow Stick is not really designed as a fast plane. I'd stick with the recommended 11x8 prop (do order more of these and maybe an extra prop shaft!) and enjoy the plane for what it is. When you're ready for more speed, you can swap all the electronics into something else.
Just remember the warning: Do your maidens in as close to zero wind as possible. I don't judge slow stick weather by whether or not I can feel the wind. I usually look at the 'turbines' on the top of my house that vent the hot air from the attic: if they are moving any faster than barely moving, I usually take another plane to the park. Not that you can't fly the SS in winds--you can once you get accustomed to it. It's just that wind pushes the SS all over the place and much of your flying becomes wind correction.
Good luck.