You don't start taking engineering courses for ME at Caltech until you're a sophomore, so your frosh year is just core and all the other "frosh classes". The aero minor is two year-long courses, which you usually take as a senior. The courseload for ME is roughly average for Caltech majors.
If you want more detailed info, check the Caltech Catalog at
Caltech 2007-2008 Course Catalog