What the heck is going on in here? I've been avoiding reading this thread all semester because I never had time to read it all... now that I'm done, I read it and WOW! This has got to be one of the most ludacris threads I've ever read!!
Breadboy,
Don't play the Fantasie! Wait a little while until your technical abilities have grown past the level at which you spend 3 months learning Fur Elise. To the rest of us on here, you're coming across like a 3 month old baby that says (if it could talk) "I've been drinking milk for 3 months, do you think I'm ready for a think, juicy beef steak?"
If you start playing advanced repertoire too soon (especially after only playing for 5 months!!!!!!) you're going to injure yourself, guaranteed -- if for no other reason than your endurance is not sufficiently trained. It is when you are tired that you are most susceptible to injury, and if you try playing something as advanced as the Impromptu, you will get fatigued (if you ever can get it past a snails' pace, that is) and even with the awesome technique you learned from Fur Elise, when you're tired, it will go out the window and then your muscles and tendons will strain to keep up with the music and you'll end up with an injury. I speak from experience here. I started playing the piano at age 11, learned the Rach prelude 3/2 my second year (which I played for a solo/ensemble festival that year and got first place and a standing ovation from 300 people, btw), spent the next few years building repertoire such as chopin waltzes, nocturnes, scherzos (Bmol and B-flat), etudes, Beethoven sonatas and Rachmaninov preludes and etudes, etc. until finally I developed a severe case of tendinitus. I had to stop playing for about a year (it hurt too much to do ANYTHING -- even relatively easy tasks like putting on socks were excruciation). Fortunately, I started practicing the next year, but not only did it take awhile to gain the proficiency I once had, but I was forced to revise my technique and learn better ways to relieve tension (which worked, and I've gone well beyond anything I could have done before). See, even though I studied with some of the best teachers in my country and had attained a technique that allowed me to play those relatively difficult pieces, it was still not enough to avoid injury.
As a performing pianist and teacher, I will make a bold statement: after playing for 5 months, I can almost guarantee beyond question that you have not attained the required technique to play the Fantasie-Impromptu at ANY level of proficiency. It's like the guy who wants to go from one side of a deep canyon to another without first constructing a bridge. Posting such a hilariously outrageous question on this forum as the one you originally posted is akin to asking an astronaut, "I'm getting better at flying my radio-controlled airplane that I learned to fly this afternoon... do you think I'm ready to pilot the next mission to space?", or still another... "I learned HTML today, do you think I'm ready to program a PHP forum to use on the internet?" I could go on and on.
You posted a horrible performance of the moonlight sonata and said you wouldn't ever perform a piece in that condition. Well, sorry to say, but despite bad rhythm, wrong notes, memory slips and wrong interpretation, the performer obviously has had multiple years of instruction at the piano. Using your own standard, why on earth would you want to work on a piece you would never be able to perform? After even 9 months (assuming it only takes you 3-4 months to learn this beast), you will not have the experience, technical facility, musical insight or physical stamina to make this piece concert ready, according to your own definition. Music does not just "happen", especially if you have not the time to put into it, as you stated you don't have time to practice.
About the whole Mozart thing... Last year I learned the Mozart Concerto in A K.488, and I'd rank it with the most difficult pieces I've done (which is saying a lot, based on other repertoire I've played recently). You can't really "make" Mozarts piano works harder than they really are -- all the musicality observations mentioned in previous posts are not arbitrary decisions based on a need to make Mozart's music more difficult. All that stuff is inherent in the music itself, and if you took time to actually study some of them with a qualified teacher, you'd see why Mozart is so difficult.
Dude, if you meant this to be funny, I must admit I had a good chuckle here and there after reading your posts, as I'm sure many others did as well.
To the rest of you reading and posting here, count your blessings -- he could be your student!

P.S. Where's youre recording??? I want to see if your self-assessment holds any weight.