I would hope that the sides of the stand offer some support. If you're floor is sloped that much, you might want to consider trimming the stand to level the bottom, or getting a different type of stand altogether. As for how far away to place the tank, that depends on how much clearance you need for anything hanging off the back. If you don't need any, then you can place the tank pretty close to the wall. I'd leave a little room regardless, though.