I had a similar problem (land sloping towards the house) with a much simpler solution. I got a free dump truck load of fill dirt from Craigslist and then graded the foundation correctly. Took an incredible amount of work by hand as I didn't rent a bobcat.
Fortunately the land was overall flat, other than the problem with it sloping in towards the house, so that was sufficient to solve the problem. It sounds like you had worse issues with your terrain.
Yeah. There was no way to slope away from the house because the house was built too low. We actually ended up draining the system into the city sewers under the street. So, I had to work with their contractors to connect it.
We removed a few tons of dirt by hand lol.....I regret not renting a bobcat.
Fortunately the land was overall flat, other than the problem with it sloping in towards the house, so that was sufficient to solve the problem. It sounds like you had worse issues with your terrain.