Horn and bassoon in unison make hardly more noise than either alone. I'd rather double high flute with low bassoon, four octaves down, and stick some contrasting material in the middle. But mostly I try to steer clear of doubling. These instruments offer a vast menu of non-legato possibilities, from nasty accented staccatissimo to gentle pulsation. Make horizontal space as well as vertical.
Silence is essential in wind music.
Extreme registers require extreme discretion from the composer, because that's where the player will most likely experience technical difficulties. But use those extreme registers. Get away from Middle C. Think of dynamics as part of the meat, not just the sprig of parsley. The horn can purr, or blast the audience out of the room. The clarinet is more capable of immense crescendi and diminuendi than are the flute, oboe, and bassoon.