How correct is this summary I'm working on so far?
Technical Resolutions: 320x192, 320x96 (double tall pixels), 320x64 (triple tall pixels), or 320x48 (quadruple tall pixels)
Playfield: 8x1, 8x2, 8x3, or 8x4 pixels (depending on resolution) of foreground & background color, foreground color can change within the scanlines on an 8x-width pixel by pixel basis.
Hardware demands the playfield to be symmetrical, but coding can overcome hardware to be asymmetrical. [See BladeJunker's guide on how collumn splitting works]
Player sprites: Up to two unique sprites, 2x1, 2x2, 2x3, or 2x4 size pixels, must be 8 2x pixels wide, can be as tall as desired. Can be copied*.
Missile 1 & 2 sprites: Single pixel that is 2x, 4x, 8x, or 16x wide, can be any height. Corresponds to relative player sprites. Can be copied*.
Ball sprite: Single pixel that is 2x, 4x, 8x, or 16x wide, can be any height. Cannot be copied.
* Whenever you copy a sprite, it shares the same x origin of the original sprite for movement, and must be offset by 32, 64, or 128 pixels and + width pixels.