I have had one, and had a similar problem with the spraybar. The water is supposed to go over the first chamber, then trickle over the divider into the second chamber, then out the outlet. The underside of the outlet is where you attach the outlet piece.
As for the powerhead elbow, that should be a snug fit. From memory, there were two elbows. One for the powerhead and one for the outlet. Make sure your not getting them round the wrong way.
If you decide to set up an internal heater, you can hide the cord under the lighthood. I had mine on the right of the tank, cord comes up, theres a gap in the plastic that I fed it through (to in between the lights and the filter), along the center of the lighthood, and then through a similar gap on the left, up and out with the power cords for the lights and powerhead.
Hope that helps, good luck with the elbow.