75 gallon into a saltwater tank?

So one thing I have found with 55 hexback tank is there is a of bunch busy work having to be done. I am constantly trimming the plants back and cleaning the glass of algae. My plans to make the 75g into another planted tank have change slightly. I am thinking I really want to make the 75g into a saltwater tank. Eventually will hope to make it into a reef tank. Since I took down the 30g planted tank because it got snails from some of the new plants I think I can make it into a sump for the 75g. The 30g DIY sump should be big enough to filter the water but I am not sure I will be able to fit a protein skimmer inside as well as the bio balls. I am still doing the calculations to make 100% sure sump will be big enough to filter the water effectively. I might end up buying a 40-50g tank on craigslist for cheap and making that in to the sump. What ever I choose it will take months to get up enough money to buy the thing I will need.