Hi Mike, I like my fish tank to stay at a constant heigth...that's just me.
Your fish tank is also going to act as your sump, so your water will go up and down a little.
Of course your tank is pretty big....you may not even notice.
Your F&D's are about 180 gals....they may only hold 40% of that, after the media is in....aprox 72 gals per bed. Even if all 4 fill at the 'same time', your only looking at 290 gals out of 1200 to 1300 plus gallons of water.

I'm just starting to use 'Bells'....so I really can't say much there. Except, I've heard only good things about Affnan's.

A 2" drain 'might be' ok....what's the odds of 'more then' 2 bells kicking in at the same time ?
You will get a 'bio' build up inside the pipe, which will slow it a little.
If you wanted to lean towards 'over size'....or if you think you may add on in the future (?).....
You could jump to 3 "....'or' .... run 2 differant drain lines. Tie two of your F&D's to their own 2'' drain, and a differant drain, for the other two beds. Might be easier then the 3 " drain.

It's cheaper to go bigger 'now'...less work and 'no kickin' yourself later'....
Bigger is better, when it comes to pick-up trucks, guns and drains..... :P and pizza's and paychecks too.