Newbie to our site, but not one to the hobby
Relying on someone else and the RO unit constantly blowing out may have gone hand-in-hand if that person had it hooked up in your filtration loop. A big no no that equals constant blowout. Some good news..........You won't need a very expensive light fixture. What you have planned sounds ok, but just a bit of concern on your tank depth with the lights you chose. They will need to penetrate that 30 inch depth. Don't need the protein skimmer. Sell it and use the bit of extra cash for the freshwater endeavor. Or, if you happen to have an outside pond, you can actually use it there. More good news.........you can still use your existing sump. And, if it is reasonable large enough, say 30 gal capacity, you can do most of your major water changes from the sump and not that much from the main tank. A shall/small school of Barbs sounds great also. You can go with a small full blown school of one of the smaller Barbs (24-36) or 5-7 Spanner T Barbs (let them grow out in that tank - they will get 5-6 inches and really cool).