no worries easy fix on the gurgling. build one of these.
http://home.nc.rr.com/stockmanreef/b...nstruction.htm
its easy, there are other versions of durso standpipes but i like this one. keep critters out, its adjustable and quiet. i am not using the air cap thing with the air line. mine is quiet with out it. but if you go with this and it is not silent enough then i would use it.
for the rise and fall of the water level, i think you are close to your max flow wise on the bulk head. might want to look into that and perhaps get the next size pump down. what size is your pump and how big is your bulk head?