No problem for the tip. I found you get better yield, better light penetration, bigger and tighter buds if you get the correct node spacing. You can also eliminate any need for pruning leaves. Although it depends on the strain to some degree, I had issues with a plant that was too stocky due to lighting being too close.
I haven't had any experience with using only the red spectrum for flowering. I've only used a combination of blue and red. The leaves always prefer to point towards the blue even if it's further away. If it were up to me I would just add a red when you switch to 12/12.