I think that before starting with pieces like that Mozart's sonata, you should try to do some mechanic exercises. Try Hanon exercises, or Czerny op.599 and 849.
Also, you should read Introduction to the Art of Playing the Pianoforte, Op.42 by Clementi, it answers a lot of questions.
Anyway, this will never be the same as having a teacher. Trust me, it is a lot different.
Hope I was helpful!
João