@Banamatic
1) Rank definitely increases for every set you complete, but the changes are pretty small nonetheless. I don't think survival would affect rank as much in this case (Garegga gave you extends every 1mil pts, but Dimahoo only gives two extends at two fixed score points). So I guess, yeah, not collecting any sets at all will keep the rank nice and easy.
2) Doesn't seem to be an exploit. Your best bet is to speedkill them before they even fire, which was probably what you did. I played a run just now, they seem to be just aimed shots...can't you tap-dodge?
3) Bullets=>Laser seems to be random. I just try to launch a lv.8 fire charge so I can at least get to his 2nd phase as fast as I can (with the really fast spread stream) since the 2nd form is relatively easier than the first.
4)This question got me. I tried doing a save-state run -just- to see if I can ever trigger the full red form, and it doesn't seem to exist.
If you want a easy 1CC, use Birthday. Her bomb is really broken.
(In case you don't know how to unlock the 4 secret characters, insert a coin in the title screen and press Up, Up, Left, Down, Down, Right, A, B, A, B, A Start)