That is absolutely stunning - great job. The Cello gives a whole different feel to the song after around the 26 second point. And the entire opening seems like it was just made for that Cello o' yours. Beautiful!
As for what you could tackle next... Hmm.. while those two you've suggested would be very interesting through your string-ability, I think you'd be capable of doing some absolutely lovely versions of say, the Cosmo Canyon Theme, or 'Life Stream' (which is easily one of my favourite songs on the OST for some reason or another).
Keep up the great work!