(snip)
'Existing aggregate' would scare me a little. Fine and dandy if your existing substrate is deep enough and drains properly. But how do you or they know? Around here, the top-tier companies scrape to undisturbed soil, reserving reusable gravel, and build back. If going to undisturbed soil is not practical (like on a lot made out of a swamp), they put the base down in layers, and roll and tamp the living hell out of it. My asphalt driveway has a dip that was pretty clearly a truck tire rut or loosely filled ditch, that they just threw sand or gravel in.