When to start a concerto?

[kentar]

I'd just like to take a gather and ask a simple question..
When would be the best time to start a concerto?

I'm currently working on:
Chopin Polonaise Militaire op. 40. no. 1
Rachmaninoff prelude in g minor op. 23 no. 5
Bach Prelude and Fugue in c-sharp minor

and a few others.. if it helps, I could play the 3 mentioned pieces at performing standards as little as 3 months.

Would now be a good time to start a concerto?
If so.. what might you recommend?
Give me your thoughts.

Thanks!
(Sorry this post was put up twice and I can't figure out how to delete the old one..)