Hi carl_h
I think you have this piece well one the way. Just a few suggestions:
Regarding the tempo, maestoso means majestic, stately and dignified, so you need to play this piece in what we call "the grand manner". Endow it with nobility.
I have the Dover edition here which gives a metronome setting of a quarter= 63 to 66. Scriabin in his own recordings sometimes ignored his own tempo markings, but this one falls into adagio which makes sense in view of maestoso. I would stick with that.
I've posted a lot of Scriabin here, but have not played Prelude 13/1. So I followed the score.
The melody is in the RH and runs through the top notes of the chords. So this requires attention to legato playing in the phrases. A good way to practice this is to play the melodic line alone without the pedal, making sure that you are connecting one note to the next to produce legato touch. Be able to sing the line in your head too. That will help in performing because you you'll be voicing the top line (which moves horizontally) while you deemphasize the other member notes of the chords which are harmonic and are more vertical in nature.
In balancing the hands, the right hand which carries the melody will be dominant, while the left hand containing the bass harmonies is accompaniment, so needs to be more subdued. Having said that, notice that in the LH there are scalar figures at times. Look, for example at measure 6 and 14. Scales in music are important and should be etched like the melody. That doesn't mean to overemphasize them, but play them enough to be heard.
Notice in measure 20 in the LH Scriabin writes two-octave slurs. Right now you treating them as staccato touch. But because the staccato markings fall within the slur markings, you're not dealing with staccato there; rather it's portato touch. The best way to play those is to apply a "downward" hand gesture in octave mold followed by an "up" hand lift-off gesture on the second octave. The down motion is a bit accented, while the upward lift-off of the second octave will be more subdued. I think of portato as not being legato where connecting notes is vital, nor do I think of it as staccato which is generally a lighter touch unless specifically marked otherwise. Portato is more of a pressing into the keys, and in slurs, still emphasizes the down motion more than in the lift-off. Portato sometimes needs some experimentation to get the right effect.
Right now I really believe the piece is over pedaled. In both hands you have moving chords and octaves. If the changes in chords and notes of the octaves are neighboring or passing tones, and if you hold the pedal down, there will be a great deal of clashing and blurring, and that's what I'm hearing now. The only time the piano will be more forgiving is if the RH is playing in the mid and high treble. But in this piece there are hardly any ledger lines in the treble, as much occurs in the tenor register. Also every piano is different, and the acoustic of the room will be different too. In the extreme case, you might want to try pedaling each beat for the most part unless a chord doesn't change. Or, if you can manage it, you can do quarter and/or half pedal releases to "spill" excess overtones if they are getting too thick. Here is the most important thing: Always play for CLARITY.
Your dynamics are fine, as is you voicing of the melody.
I hope this helps.
David
Topic: Skrjabin - Prelude Op. 13 No. 1 in C major: Maestoso