Room for a large sump? Probably anywhere from 75-125 gallon... Then you can go many different ways with filtration options. Skimmer section, could do a nice fuge, reactors, etc... Would love to have that size tank. I run a 20 gallon sump on my 40 gallon tank...
A fuge a just a place to put rocks and macros for extra bio filtration and natural nutrient removal. Not real hard, I'll dig up a link to a couple good articles on sumps and fuges and post it here for you to read through.
Well how is your current wet/dry set up? A large sump shouldn't be too much different but will give you options for filtration. Just research different sump designs and see what would help you the best... I have a simple design, input-skimmer section-return section.
I have a 220 system and use a refugium made by ADHI. It's about 60 gallons and fits under the tank in my Stand almost like a glove. Really happy with it. It's kind of a mess at the moment but here are pictures of the various chambers. I use an external pump but you could use the last chamber for an internal pump if you want it. For various reasons I prefer the external pumps.