I've never been a part of a high school orchestra or band, so I don't know what high school flautists and clarinetists are capable of. The musicians in my college band could certainly have played it, but I thought it safer just to ask. At any rate, I threw out that section and did something completely different (and far better), so it doesn't even matter!
As for the key signatures, I'm finding I don't need to modulate for this piece! There's a lot of possibilities and variety just in moving from major to minor and everywhere in between. This is probably the best thing I've ever written... in fact, though I came in thinking, "I'll just do my best and have an extra something for my resumé," now I'm beginning to realize I could very well win the competition - and that's very exciting, even just to be composing at this level.