How to set up a marine tank for 2 gsp

[8rheams]

I have 2 gsp currently in a 15 gallon and am looking to upgrade them to a much larger marine set up as I know that it’s cheaper to run a full marine tank than a high salinity brackish tank. I’m experienced with freshwater fish but not salt water and all my salt water research has been confusing me tbh! A lot of you tube videos seem to say to find someone’s set up that you like and copy it. Would any one be able to share their set up for their gsp if in full marine? I.e. if use a protein skimmer, refractor, sump, refugium etc and how often water changes are needed on your set up. Any help is massively appreciated!