Piano Forum

Concerning the concerto, I agree with most other people who have responded.  Going from Moonlight Sonata to Grieg's Concerto is silly--for a couple reasons.  The only time you should learn a concerto is when you will actually be playing it with an orchestra.  Is there an orchestra who would be willing to play with you?  If not, then there is very little point in learning a concerto.  You can have someone else do a two-piano duet with you, but it won't sound the way a concerto is supposed to.  If Moonlight Sonata third movement is the most difficult piece you have learned, it probably means you haven't tackled much romantic repertoire, as most pieces by Chopin, Rachmaninoff, Brahms, etc. are of equal or greater difficulty than the Sonata.  It is commendable that you have learned an entire Sonata, as it shows you can play a lengthy piece of music (presumably) from start to finish without error.  Get a few more sonatas under your belt, along with several studies and a well-rounded repertoire (from the romantic period) before you look think of seriously studying Grieg's concerto.

Yes, it is considered one of the easier concerti, but that's compared to other popular, "big-sounding" concerti such as those by Tchaikovsky, Rachmaninoff, Brahms, Prokofiev, Beethoven, and so on.  Compared to other more difficult concerti, Grieg's isn't too demanding, but compared to most solo piano pieces, it's a huge undertaking.  Tremendous stamina and technical skill is required in many places throughout the concerto, which may be difficult to recognize simply from listening to a recording of it.  It's easy to fall in love with this piece--it's quite beautiful, and doesn't sound too difficult, but concerti are very good at covering up a lot of the nuances of the piano playing with the orchestral parts.

The sonata is not an easy piece, nor is it short, but Grieg's concerto is a good 7 minutes longer, and is on a totally different level in terms of difficulty.  The concerto is considered a collegiate level piece (as with most concerti, and with good reason) whereas the sonata is probably a level 8 piece, as you said.  Level 8 would be like a late high school piece, meaning there is a year or two gap (for most people) between the sonata and the concerto.  Don't be in any hurry to learn pieces that are beyond your abilities.  It's better to learn pieces that are challenging, but more because they are different to what you've learned in the past than because they are clearly well above the difficulty of your learned repertoire.  It's good to have a well-rounded music education, so make sure you have learned pieces by Mozart, Bach, Chopin, Rachmaninoff, Brahms, Haydn, etc.--representative composers from baroque, classical and romantic periods.  Grieg does fit in there, but maybe you could try learning an easier piece by him first, such as one from his lyric suite--some of these are quite challening and fun to play.

Hope my advice has helped.  Bottom line:  Don't learn the concerto, YET.