Can you be a bit more specific on the gravity room?
I know scarefactory makes a few cool anti gravity props, are those the effects you're looking for?
If their reputation scares you, just ask them for the mechanism "skeleton" and use your own props/pieces.
As for ball pit......the idea is COOL. However, with plastic balls it may be almost impossible. Individually the balls aren't heavy but collectively if you had a vacuum large enough to lift enough balls for it to notice.....you would be ripping the hair off your customers heads or make it impossible for them to breathe.....HOWEVER, why not use a TON of water balloons? They're similar in size and shape when inflated. They're cheaper. And there's a few ways to lift them I can think of;
1) vacuum like you said, a much smaller one would be needed and it'd be safer and more cost efficient.
2) fans!! If you get a bunch of flat fans and build a platform on the floor and have them recessed in areas off the walking path and some from the ceiling at different angles, to throw the balloons around, you'll be set, you can even make fake ball piles using the original balls you want to use and make "covers" out of them for the fans.
3) HI-FLOAT! From all the party planning, DJ-ing, and decorations I do for parties a million times a year, this is hands down my FAVORITE idea! Ok, so there's this product called Hi-Float for latex balloons, it's basically a sealant for balloons that make it so that helium doesn't leak out of them for a LONG time. You won't go through too much helium since the balloons are so small, and use fans on the ceiling to keep them going up and down. It isn't as defined or timed as a vacuum, but it's much cheaper and will still look really cool. And cold air going down your customers backs is always an added creep factor