Explanation: Music arranging is about dividing the parts between melody, harmony, counterpoint and rhythm. Instruments such as strings, saxophones, lead guitars and the like will bear most of the counterpoint burden.
Based on what you wrote in the roadmap, you should know which instrument plays what (M-H-C-R) and when. As you see, by preparing that counterpoint chart, you have already done most of the work. Here, it's simply copying. Remember that these instruments, for variation purposes, can play rhythm, harmony, or melody backup as well. Don't be afraid to adjust your original roadmap if the inspiration hits you.
An important rule of thumb here is to keep your harmony parts fresh. Send the counterpoint melodies to different instruments. Vary the " weight," the amount of instruments playing each part. Keep the musical story unfolding.
Next: 11. backing vocals.