I would like to align the view straight on to a face, perpendicular to the normal. How do I align the 3D viewport to the face of a mesh?
In edit mode with a face selected press ShiftNumPad 7 That will align the view to the active face.
If you want to align the view to a different axis relitave to the face, ShiftNumPad 1 and ShiftNumPad 3 can be used. Ctrl can be added to any of the key combinations to invert the view.
For example, CtrlShiftNumPad 7 will look at the "back" of a face.
Do note that there can be faces that are not flat. In such cases the view will be aligned to the face, but any manipulation will warp the face.
Yes, ⇧ ShiftNumpad 7 will do this.
You may end up with a strange rotation around the view's local Z, in which case ⎈ Ctrl⇧ Shift MW can be used to roll the view to a more preferred orientation.
Also note that ⇧ ShiftNumpad 1 and ⇧ ShiftNumpad 3 can be used to align the view parallel to the normal. ⎈ Ctrl can be added in to align to the opposite side.