One part nutrients are everything in one part.ybody
Two part nutrients are split into two usually a grow and bloom where you use both but more grow during veg and more bloom during flower.
Three part nutrients are split into three parts. Typically one part for nitrogen, one part for micronutients and one part for potassium and phosphorous. You mix them in different quantities depending on the plants stage of growth.
one, two, and three part nutrients will all typically supply everything a plant needs to grow.
Additives and boosters are things that people use to supplement their grow. They have names like bud blaster, cha ching, silica blast, etc... and are not intended as a main source of plant nutrition. Until you've mastered a couple of grows it's best to keep things simple and stick with just the base nutrients.
Promix HP already has perlite in it so if you add more it's good to use the chunky perlite not the fine.
Just off the top of my head
2 parts promix
1 part perlite
1 part worm castings
1 part compost
But why not keep it simple for now and just buy some Happy Frog or other good quality ready to go soil?