There are some great stickie posts under the saltwater subsections, they will be a great help to you!
ASnd to answer some of your questions:
Yes, for a 30g a hang on back filter or even a canister would be ok.
A skimmer wouldnt really be needed if you do your weekly water changes, that will remove all the bad stuff and replenish the elements that you need for corals, so no need for dosing a tank with anything.
A sump is up to you. A drilled tank just cries out for a sump and they are so easy you'd be surprised. But a 30g most likely wont be drilled so I would, if it were me, leave the sump out of the equation.
I ran a 29g as my first salt tank and ran it with an aquaclear hang on back, heater and some cheap 4 bulb t5 lights and had alot of success with my corals. Did my weekly water changes and everything thrived.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.