Before approaching the concerto, I would have a go at the Rondo Op.14. If you can master that, you are well on your way to coping with the demands of the concerto.Judging by your current rep, you might be a year or more away, but it is always good to have something to aim for.Personally I find the Weber PC's superior, albeit they are almost cut from the same cloth.Thal
It's pretty hard for us to tell how developed your technique is from a list of pieces you have recently played. If you played those pieces in a sloppy, musically haphazard manner with poor control of tone, rhythm, and phrasing, you could easily be four or five years of good-quality study away from playing the G minor concerto well. If you played those pieces with good taste, nimble execution, and considerable attention to stylistic detail, you might be able to give a fantastic performance of the G minor concerto within six months! Post a video of your playing! I would say the D minor piano trio would give you an accurate idea of how it feels to play virtuoso music by Mendelssohn in a real-time setting with other musicians.
I agree, or the Weber Rondo in in C from the Sonata, Hummel Rondo in C, maybe a look at the Clementi Sonatas. Try various movements from the Beethoven concerti 1, 2, or 3.Kitty on the Keys