Keep in mind that when you run a motion, it's meant to be a fairly balanced offense. So even if you try to give somebody 1/2 of the shots, it likely won't be close to that.
With that in mind, try to keep the starters all around the same to begin with. Say 10. Give your best guy an extra point or two, and take away a point or 2 for the weakest offensive starter. Then with the bench, do the same and start at something like 5. As you play more games and see more patterns, keep adjusting as you see fit.
As far as what make a better offensive player and who you should give the most distro to? That's a combo of IQ, ath/spd, lp/per, and bh to varying extents for each position. Let's use Butler on your team as an example. He has a good LP at 79 for a d2 C. But his ath/spd is 23/17 and his motion IQ is a C. If he's clumsy, weak, and slow, it doesn't matter much how good his moves are, he's not going to be your #1 offensive option this season. If his ath/spd were 50/30 with the 79 LP and a better IQ, then he might be the best option in some matchups.
Good luck.