Thank you everyone, that's really helpful! F#m - that sounds like my intended approach too! It's quite hard when I'm still only learning something which, for me, is quite difficult, to know how it will sound when it's all a bit more fluent.
Well Ive been playing it since 1962 ! Indeed for my ALCM Dip in 1963. If you listen to You Tube performances you will see there are many with a big variation in tempo. Variations from 2min 40s to over 4 min 30s. I like it to keep it flowing but Andras Schiff for example is a bit too quick. I like Alicia Larrocha at 3mins 6s is my ideal. The longer ones drag rather. I don't think we really know what Mendelssohn intended ! Of course if you havent got the basics secure yet, you may want it at a slower speed. Good luck.