A wall that is less than four feet high doesn't need a footer or mortar. It will stand for years with minimum maintenance.
Don't try to retain all of the earth with just one wall. Follow the grade and make different steps. Curve the wall to follow the natural lie of the land, this will mean a lot less work.
Nasturtiums are good for the first year. Later you can use any plant that will trail, English Ivy, Creeping Jenny, or Vinca.
Take a look at retaining walls as you drive around and you will see many examples of walls that are falling over because they were built like this.
Note that each stone is tilted back. That way the earth pressure has to lift the stones to move them. If you put each stone in level then they can still slide out.