Okay, I HAVE to put in my .02 here. I played French Horn in high school and college as I moved from one state to another. i went from being the concertmaster in the youth orchestra to French Horn. I chose French Horn because I liked the sound and because my younger briother already played trumpet. I switched to trumpet later (although i played my brother's horn at home sometimes, and I played trumpet during marching season.) I have experience with both. French horn requires more finesse in the approach and has a very extensive low range. If memory serves, there is another octave and a half or so below the low G that you know from trumpet before you get to the pedal tones. Now, you usually don't see that written in band charts, but if you play with a symphony, those notes are common (at least that was my experience "back in the day") I have ALSO seen many band directors steering students toward instruments that they need in their ensemble and talking them out of playing the instrument that the student wants to play. I see a number of those students discontinuing band in a few years. It is a difficult line the band director walks. While I understand their need to make themselves look good through their ensemble, I wonder how many talented players we lose. My advice to the OP is to play what YOU want to play. If you can say to yourself, "okay, I will play French Horn here and trumpet there" and get support from your band director, then fine. However, if trumpet is the only instrument that holds interest, there comes a time when you have to follow your muse. That is not to say that you might not enjoy the stimulus of a second instrument if both are possible. In the final analysis it is something the OP will need to decide.