If you are dealing with outdoor storage and there is little consequence of settlement (beyond what you could mitigate by importing a few more loads of aggregate), I'd just remove topsoil and if it proofrolls under a fully-loaded 10t dump truck place my aggregate. I'm not sure you need the geotextile/geogrid if the subgrade proofrolls.
On the other hand, if the subgrade doesn't proofroll, you may want to use a geotextile. I'd consider a woven geotextile (e.g., Mirafi 500x) and then place a minimum 12 in subbase.
Just out of curiousity; how much slope is there on this site? If there is no slope, infiltrating rainwater will just fully soak into the open-graded aggregate. Not sure how rapidly the water will soak into the sandy loam layer (I could guess, but then again. . . ) but if there is construction traffic on a saturated subgrade, you'll loose strength. If you can't provide internal drainage to the subbase, I'd use the geotextile whether you pass a proofroll or not.
Good luck.
f-d, c.p.g., p.e.
¡papá gordo ain’t no madre flaca!