Half of our home is below grade and it's wonderful....we don't heat or cool the lower level and it hangs between 60 and 78 all year round. It is also much quieter.

I hope it's a southern facing slope for passive solar gain, and don't put any decks or anything over the windows or it will feel like a basement.

The part underground is the north side. So, yes, the slope is facing south as is the front of the home.

How can it be underground if it's going to be a crawl space?

Some areas will require a drain field that abuts the upslope side. In other words, a reverse slope on the north side which causes the downhill flow to be directed away from the building, to the side yards too resume the natural flow to the street.
Also, the north side foundation being higher than 2'6," will be engineered as a retaining wall, so a french drain will be needed to address the hydrology.

Thank you. We backed out and are back to square one. I have severe mold sensitivity. All the talk about the complicated drain systems did me in. Thank you all for responding.