Make sure you contact your city hall for permission and make sure it's a place where flooding is rare.
I would also look up help from the internet first.
Meh, I don't really need to. I live on top of a hill and the area around my house (except for my road and the neighbor's houses) is pretty much just woods/forest. I could hide stuff down there that no one would ever find.
start building up rather than out. make a gigantic skyscraper that uses most of your pieces but doesn't take up much floorspace.
This sounds like a good idea too, but probably only for bricks of the same type/size. That way, as I needed them for building, I could simply pull the m off of the skyscraper one by one.