IMO the best filtration for a reef is live rock, live sand, a "good" protein skimmer and a refuge.
I wouldn't replace the bioballs with LR rubble but I would remove them. Adding live rock to the tank will take the place of the wet/dry although you will most likely cycle again.
A 75g refuge on a 180g tank would be nice. I have always found sumps very useful so personally I'd turn the wet/dry into a sump.