A really quick way to bake this kind of info into your brain... is stick a polaroid back on and grab a notepad. There's something about taking a shot, examining it, coming up with what seems the correct next step, and trying it out instantly... vs. shooting a roll and processing and trying to suss out notes for every frame. In the pre-digital days it was a dynamite way to learn some more advanced stuff very quickly or test your crazier ideas.
There's still 2 decent flavors of pack film available after all... and peeling those things always brings back memories (for me anyway).
EDIT: you can likely get a hassy polaroid back for next to nothing thee days, if you don't have one...
You can reduce the output by using a layer or two of lens tissue over the sub flash. Main flash too if you wish. Since you're dealing with guide numbers, there's a bit of testing to be done. The gn can get you close, but it' a guide not actual.
John's tissue idea is really useful. When I'm at a bar with the mrs., I'm always tearing off little strips of bar napkin and licking the edge to cover the flash on her phone - if you curve 'em enough you get instant soft-box (OK, she's a always posting pics of dinner on facebook, it's not as effective for group shots but makes closeups really pretty...)