The garage idea is good but that will still leave you with a 26% grade assuming you are not meandering the drive. It might be worth looking at the legal aspect of building something this steep. Will you be liable when little Johnny loses control of Mom's hummer at the bottom of the drive...
Typically, sewer smell is incresed at drop manholes. That is, where there is an significant elevation change between the inlet and outlet. This can be reduced by making sure that the vertical pipe on the inlet extends nearly to the bottom. This should reduce the spraying/splashing. Also...
As a Construction Engineer on State projects I can tell you that the more information the better. The cross sections should always show utility information. Of course a good contract and set of plans will have language that states the contractor should field verify all existing utilities...
