You could have made things a little easier if you had built the toe kick (out of 2X4's), attached that to the floor (leveling the toe kick), then built the cabinet carcase and set the boxes on top of the toe kick.
My suggestion to anyone who is building their cabinets: Build your cabinets out of plywood, not particle board even you you can get the high density cabinet grade particle board. Particle board is very heavy. Free 32mm Frameless Cabinet Plans
for an easy cabinet box to build. You can pocket screw a face frame to a 32mm system. The toe kick plans make installing the cabinet run very easy and you have a level flat base to attach the base cabinets to. Building the toe kick separate will also allow you to route heat/air ducts, plumbing, gas lines, electrical wiring under the cabinets. You can buy a simple hole jig from many woodworking outfits to drill your shelf pin holes. This is the one I have, it's inexpensive and takes up little space and I have used to drill shelf holes in a 24" High Wall cab up to a 84" High Tall pantry cabinet (24" deep):Jig-It Shelving Jig
comes with a self centering 1/4" bit (buy 1/4" shelf pins) OR 5mm bit (5mm shelf pins). Works on traditional framed or Euro frameless. I have both bits because I had to use some 5mm shelf pins. You can buy the drill bit systems separate from the jig. The jig will hold two bits in the black handle.These 1/4" shelf supports
have a hole in them and you can drill a matching pilot hole in the bottom of the shelf and put a screw in to hold the shelf in place. The cushions are for glass shelves. I would also recommend metal shelf support/pins over plastic ones. I've got both plastic and metal in the Class C. I can load a shelf down more with the metal than the plastic one. The plastic ones support with no problem until we travel down the road. Then they shear out of the holes.
Also you can spend a bit more $$ and buy a Veritas 32mm Cabinet System