i don't know much regarding the deaths of the crocs and so don't hold any of it as factual its all from memory and was a while ago.
pretty sure the imports all died suddenly and whilst in quarantine in the off-facilities of the reptile house, after only just arriving. they were all small, juvenile crocodiles.
one reason that breeding has not yet been attempted is because the zoo male is still too small to live with the female. last i went i'm pretty sure only the large croc was on exhibit, same as always.
the exhibit isn't bad but could definitely be better. i will try to remember to get photos next visit but will describe it to you in the meantime.
melbournes reptile house is circular. on the exterior wall are larger exhibits on the interior wall smaller ones. the inside wall exhibits can be accessed from above the enclosures as the very center of the house is an off-limits area with many, many of display reptiles. i'm not 100% but i don't think the outer exhibits can be accessed from above - there is no walkway behind them that i know of. instead, to access the enclosure, i believe the keepers simply open up the glass windows at the front which are actually in steel frames and hinged with a lock at the bottom.
two of the three largest of these outer exhibits are utilised by the zoos cocodilians.
the interiors feature relatively shallow pools (500cm?) and i'm guessing the entire space is maybe 5m X 10m divided with a little over half the area to water. but this is rough guesswork. the pools do not have underwater viewing - instead one looks down to the water surface below. the ground is mostly pebble infused concrete, though i'm quite certain there is sand areas for digging and laying eggs. lots of live plants, a waterfall and the rear area of the land space appears to have natural light streaming from a skylight (though most of the area is illuminated artificially).
probably a terrible, time wasting description, i'll try to take some photos.