For my 2 cents worth: if you can do two bottom drains, go for it. But at
least one. As for the skimmer, I find mine to be invaluable for a number of
reasons in addition to its skimming capabilities: it's also a good place to
put my salt when I want to add some, because the fish can't get to it and
burn themselves. It's also a good place to put my thermometer to keep track
of the temp, without it being out in the sun. It's a nice place to add meds
or water treatment staples (like de-chlor). I can stick my water hose in
there for water changes without disturbing the fish or the plants. There are
many benefits to having a deep well that the fish can't get to.

Lee