INDIAN SANDSTONE PAVING

Hi,
 I will be doing the back yard 5 meters  by 8,with Indian sandstone

30 cm along the long 8 meter sides I will use large pebbles as a water drain and to soften the edges .|
This way I would not need to install a storm drains.does this sound okay.
 My garden is fairly firm .I will use hardcore, 

I am not sure how many tons I would need and which type to use.
And after it is wacked down how thick should it be ?

Also can I lay the slabs directly on to hardcore ,after its wracked with out sand and cement, i would use Rompox as grout filler, or are there other options

Or would I need a mix like roadstones 36 hour trowel ready mix, I reckon I would need 2 cubic meters of this if I used it.If it was about 5 cm thick
As I would cover the entire slab not just 5 dabs.

Thanks.