How far from the foundation and how deep should a French drain be?
Location

Since the water generally comes from outside the home's footprint, drain tile is usually installed along the footing (inside, outside, or both, depending on the situation). Whether you need interior circuits in your case is uncertain. 

Depth

You don't want your drain to work harder than necessary, so it shouldn't be deeper than necessary. They're typically installed slightly below the underside of a basement slab, for example, or just below the top of the footing along which it resides. 

Drainage Media

Clean (washed) rock is important, but size isn't so critical. More critical is that you protect against silting. Fabric either wrapped directly around the pipe or laid over the washed rock medium helps prevent the surrounding soil from infiltrating the pipe and clogging it over time.