Soooo I finally saved up all my birthday money! CHI-CHANG!

Sorry Im super pumped!
Im 13 so bear with me here.
And the questions begin.
I have a 30 gallon tank with the light and powerfilter. I think Im going to start off with a
FOWLR tank. I plan on going to petsmart tomorrow and picking up some supplies, such as:
Aqueon circulation pump (500 or 700? Any ideas? And how many?)
A hydrometer
API test kit
Aragonite sand
Instant ocean salt
Then I plan on getting 5 pounds of live rock and 25 pounds of dry rock in a couple days at my
LFS. Anything I have left out?
My main questions are about the water. I don't plan on getting an
RO/
DI unit anytime soon, so until then where do I get the water from? I mentioned distilled water to my mom and she said thats what you can buy at the grocery store. Is that correct? Do you fill up buckets with that type of water then mix it with salt and put it in the tank to get started? Or can I mix it up in the tank to start off? If you cant already tell, Im pretty confused about the whole water situation. LOL!
Soooo many questions!