Gwern has a great write-up on spaced repetition [0] which you might find useful. He addresses your questions and introduces several other considerations in addi

Gwern has a great write-up on spaced repetition [0] which you might find useful. He addresses your questions and introduces several other considerations in addition. [0] http://www.gwern.net/Spaced%20repetition http://www.gwern.net/Spaced%20repetition