For what it's worth, I don't use biscuits or dowels for edge
joining, as the glue provides more strength than the wood. Biscuits
or dowells are there solely for allignment. And with 2-4 inch boards,
I don't use anything but glue. That said, the above comments are very
useful if you do use a biscuit cutter.
I have a 13" planer, and when I have a 16 inch board to make, I use
glue, and a load of clamps. Some to squeeze the joint, smaller ones
on the ends to keep the edges flush ( one per joint, each side ), and
cauls if needed for the middle. After drying overnight, I use a plane
to get the big chunks down, a belt sander if I get lazy, and then a
ROS and finally hand sand paper to finish. I keep forgetting to use
my scraper, but am usually impressed when I do use it.
I do use dowels when joining longer boards, just to make the
assembly easier to handle. It's a race to get the joint glued,
alligned and clamped within the open time of the glue, and the dowels
seem to help there.
Hope this helps.