1. When I draw with the brush tool the stroke shows as semi opaque until I lift my pen from the tablet at which point it changes to solid. I can't figure out where to change this setting - as well as being distracting, it takes a moment for it to process the switch (which doesn't work well with the sketchy style I'm trying for!). I've got smoothing set to 0%. How do I stop this from happening?
2. Is there a way to better mimick pencil strokes? I've enabled pressure sensitivity but I also want the pressure to control opacity so lighter strokes are less opaque. I'm using the brush tool since the pencil tool doesn't seem to allow pressure sensitivity and smoothens my stroke even when smoothing is set to 0%.
What version of Animate are you using? If you're on one of the newer ones, you might like what object drawing can do for you. Since Animate is a vector based app, there isn't really true "opacity" in the drawing system, unless you use layers. A cool way to get around this limitation is to use a mix of object drawing and fill opacity.
First, press J to toggle object drawing, this turns each stroke into a small object once drawn.
second, go to the color panel (Window/Color) and turn the Alpha channel down.
From here you can much more easily sketch stuff out!
In all honesty though, if all you're looking to do is sketching without any buffer time and more realistic looking tools, something like Photoshop is probably much more suited for the job.