Sounds like you have a good plan on the back fill. Make sure before covering the rock with soil the cover it with fabric so it keeps it separated.
You will want to dig down below your normal frost line about 6 -8" and pack it with crushed gravel. Add 1" of sand on top of it. Make sure it is level, level , level. Your first row of block should be below grade and use blocks that you can pin together. do not rely on the blocks with the lip on the rear for anything over a couple of feet high. By pinning the blocks together it will keep them in place for a long time.
Here is a video that shows some of the reasons retaining wall fail
Good luck with it and post some pictures when it is done
