30 gallon SW questions

You can put a sump on any size tank. You'd need to either drill and plumb the tank for the sump or get an overflow box. You would need a couple bags of argonite sand($15-$25 for 1 20lbs bags) Some rock dry rock online runs around $2.xx pound some places online offer free shipping when you get 20lbs+ LFS dry rock price in my area is $3.99 per pound. Salt mix $40-50 for 200 gallons worth, Lighting type doesn't really matter if your not planning to stock anything besides fish. Most SW fish like some water movement so 1 or 2 circulation pumps @ $20-$30ea. SW tests around $50ish, refractometer $30-40,Then your usual stuff heater, thermometer etc. Additional pump if your doing a sump, additional tank if its DIY sump along with some pieces of glass or acrylic for baffles, media, additional light if your going to do a sump/fuge combo.

Any idea on what you want to stock in the tank?

You'll want a sump/fuge to sustain a copepod population for a manderin. Hydrometers are pretty inaccurate and can be off a few points, refractometer is more precise. The $20 test kit only contains ph, nitrites, nitrates, and ammonia tests, need additional tests for calcium, kh, phosphates.

Mandarins are tough to get eating frozen or prepared foods. They will decimate a pod population very quickly then starve to death. I agree you will want a sump to have a safe place for pods to grow and breed.

Even without wanting a mandarin, you could do a SW tank with out a sump, however I would never consider it a waste of time. The advantages of having a sump are to numerous.