Same, I think it's way more efficient to do your storyboarding within SFM if you're not sure what you want to do. Blocking is exactly what you want to do. You dont even need to put your models in poses, just throw the static pose there and focus on camera/shot changes and times. Guestimate how long each shot should take, and maybe add some animation to the location (root translate) of the model, so you can get a feel of how long it should take for them to move from A to B.
It'll look like crap, but then you keep fleshing it out. Also, keep it super short. Like, you said you've done test animations, but maybe try making a quick, 10 second scene for practice before you move on to any projects with heavy animations or ambitious goals.