1) you don't have to do it like this. simply feed all the supported coal generators from one conveyor belt and split coal into the generators with MK1 belt. Eventually all generators will be saturated and working fine.
2) to split one 120 item per minute belt (ipm) to 10 equal 12 itm, you need the following:
incoming MK2 belt to a merger
outgoing one MK3 belt to a splitter
outgoing two MK2 belts to two splitters
out of each of these, outgoing three MK1 belts (total of 6 belts)
each of these MK1 belts will go in a splitter, and out of THESE splitters, two MK1 belts out.
That is 12 belts coming out in the end.
Wrap the external ones back to the original merger and bring them in, so that the initial merger inow bringing in the 120ipm belt, and two MK1 belts out of the last splitters.
These incoming MK1 belts will be fed back in, and the MK3 belt after th emerger will have now 140 itm, which are split again 12 way with the two of the shares going back in. Eventually the 10 remaining outgoing belts have very very close to 12itm deliveries.