Ok, yeah, I would definately ditch that plumbing for the drains. Those 90 degree barb fittings and the other barb fittings reduce flow efficiency very quickly so I would try to stay away from that stuff if you can. It's fine for your return plumbing, I just don't like it for drains. When it comes to elbows/90 degree fittings, I like to use the "long sweep 90's". They have a long sweeping curve to them instead of a sharp turn so it's better for effiency. That's what I'm using on my build. I also incorporated some Spa Flex Pipe (flexible pvc pipe) for part of my drains which is kind of nice. It just gives you a little flexibilty when putting things together or eliminated having to use 90's in some cases. My whole return line will be ran with it.
The best way to measure your bulkeads is to gauge the diameter of the inside of the bulkhead at it's smallest point. Just so I'm clear...the tank has two drain holes and one return, correct?