when i sectioned mine, i started by not brushing my hair for a day or so, and it seemed to separate into reasonably sized pieces.... then i just went at it with tnr! and after it is tnr'd you can still separate ones that came out funny, and adjust as you need to... its really great to have a variety of sizes, but thats all personal preference..... i kinda worried about the sectioning and sizes at first, got all panicked and such, but i realized that in the end, they are all going to be awesome and as long as you love them the way they are, there isn't really a right or wrong way
good luck!!! you are in for the journey of a lifetime!!