Start of Symphony movement

An effective exposition of two themes!  A masculine, assertive theme in C minor, and a feminine, contrasting, and lyrical (and longer and more drawn out) theme in the relative major, Eb major.  You seem to have a good sense of contrast in this symphony attempt.  Now all you would need is a development section and a recapitulation where both the masculine and feminine themes are restated, both in C minor this time.  With those elements you'd have a complete sonata form movement.  But what you have so far is great!  (The horn part being in Eb seems more appropriate now because this actually is in Eb major/C minor - although, note that in the C minor parts, if using a natural horn, a horn in C would be more appropriate - then in the Eb section they could switch their crook to Eb horn)