As far as dividing it up, it really comes down to personal preference as far as I can tell. I prefer to combine all my acid simmers and reduce the solution to a small enough volume that it will fit in one vessel. Splitting it between several extraction vessels requires a little more effort, since you have to do pulls on multiple jars rather than just one.
Just keep pulling until nothing freeze precipitates anymore. Then do another pull or two, evaporate the solvent to less than half its original volume, and try freeze precipitating again.
Which tek do you plan on using? Cyb's teks, which recommend adding salt before performing the NPS pulls, seem to make it easier to pull as much DMT as possible in fewer pulls due to the higher ionic strength of the mixture.
The color of the final product really doesn't represent the purity of the material, as is explained in
this thread. But if you are really worried about the color of your DMT, read up on decolorizing with carbon on the
"Recrystallization" wiki page. In my experience/opinion, recrystallization is the only way to go if purity is what you seek. Very quick, very easy, and
highly effective. But decolorizing is purely aesthetic, and nine times out of ten I don't even bother with it.