1. Yes, it will mix much better this way think about it
2. No, Driving highway then turning the car off for a few hours then back on was best for cleaning. Like Driving to work and back. So there is no need to need to waste it all. Just drive normally. If you use the whole bottle you should wait until a tank or two before you change your oil.
3. The SAE Paper showed that lower dilution levels of PEA still cleaned just slower than higher concentrations, this is over 3000+ miles, you can put 6oz of product in per 20 Gallons.
The bottle lists a shock dose of putting the whole bottle in at once, it will clean but not as much as putting a smaller amount over time. Anything that cleans instantly you do not want as it can cause more issues then you want.
With 6oz you are looking at 0.070% - 0.117% PEA Concentration with Redline Si-1 in 20 Gal