One question was:
"Does it matter what side of the imaging sheet you use to stamp on?"
No. There is a smooth and rough side and on the packaging they suggest what side to use based on what type of ink you are using, but from my experience both sides work just about the same and clean up about the same as well. Most of the ink I use is Palette, and it wipes off with a damp paper towel or baby wipe. I have some black Ranger Archival ink that doesn't clean up as easily, but I just dab a bit of Stazon cleaner on a towel and it comes off perfectly.
"Why the 90* angle?"
This is the key ensuring your block and stamp are always in the same position. Because the 90* angle never changes even if your imaging sheet is crooked and thus the way you line up your Stamp-a-ma-jig is crooked, it assures you of a consistent placement of your block and stamp thus giving you a perfectly stamped image where you want it. The 90* angle gives your block a place to rest that can't be changed by accidentally moving your hand like you can stamping with out it.
I hope those answers made sense to you! Thanks for all your feedback and feel free to ask anything else and I'll do my best to answer you! :)