How high can I pour cement against my house
It depends on how the exterior foundation wall is constructed. 

If it’s solid wythe brick and the brick extends down to the footing, I’d keep the top of the slab about one brick course below the interior floor surface. 

If it’s solid wythe brick and extends down to a concrete stem wall, I’d keep the top of the slab about 1” below the top of the stem wall. The brick will be mortared to the top of the stem wall and it will crack and separate from the stem wall. This will allow moisture to enter your crawl space. The reason it’s not a problem now is because it’s a vertical joint and the ground is probably sloping away from the joint. As soon as you pour a slab against the wall, you’ll be “holding” water against the house and the crack, which will allow it to leak. 

If it’s brick veneer, it should have weep holes and I’d keep the slab about 1” below the weep holes or about 1” below the concrete ledge on the stem wall that the veneer is sitting on...whichever is lower. 

Remember, concrete is largest the day it’s poured. It will continue to shrink as it dries. (It may expand during freezing weather, but it’s minor compared to the drying process.) So, it will not put pressure (stress) on your exterior wall, unless you have a basement.