Z1 - you only use this once in a while (this is your base coat).
Z2 - Polish which goes on top of Z1
Z6 - Spray to solidify the "layer"
Z5 - Minor Scratch/swirl cover-up polish
that's all you need! Z2-Z6-Z7 are really the three ones you will ever use. Z1 is very rarely used...you use it the very first time and after 10 (iirc) coats of Z2 or Z5 or alternating coats of Z2 or Z5, you need to put Z1 on again.