What kind of filtration do you currently own for the 180g?
I want to setup a sump for my 120g, but there are concerns about water spilling if the electricity turns off. Since your tank is not drilled (my assumption), then you have to get an overflow box. Or you can just tear down your tank and go drill it. The overflow box will continue to drain water from your tank to your sump (via siphoning tubes), but your water pump will not get the water back to your bank (due to the electricity being off). I think there are ways to counter this, but I have not researched that part yet.
Some of the sumps with bioballs do not get spills though because the water level for the sumps are lower for these wet/dry filters. A refugium with plants are definitely possible and have been done.
For my 120g, I wanted to get 2 Fluval FX5 canister filters with an Aquafuge (hob refugium) so that I don't have take care of the plant maintenance in a remote area instead of a large 120g. Currently (before my sump/refugium idea), I have 2 Aquaclear 110s with Korolia circulation pumps. HOB filters does not help CO2 system. Low light plants are do-able though.
I can definitely see a planted sump/refugium easier to care for plants.