I HIGHLY recommend a pre-drilled reef ready tank. Your incidence of flooding will be drastically reduced going with a reef ready tank. You won't even know to thank me for this suggestion because you won't have experienced the overflow box flooding that I'm talking about.
A protein skimmer is way up on the list of important pieces of equipment. I would recommend the AquaC Remora for a small tank like a 38.
20g sump is fine. Just make sure you don't use the entire volume with operating water. You need to leave enough 'vacant' volume to accommodate water flowing out of the display above during a power outage. A sump is a tank beneath your display. It is a great place to keep the unsightly equipment that would normally be kept in your display, ie: heater, skimmer, float switch for automatic topoff, carbon, phosban, etc.
Heater - use two for redundancy. This is the #1 piece of equipment to fail in our hobby. Use two 75w heaters. Technically all you need is one single 150w heater, but the above statement WILL effect you at some time in the future. If the heater fails in the 'on' position, it will cook your tank. If it fails in the 'off' position, it will get drastically cold. Two smaller heaters (even two 50w heaters is fine), will not be sufficient to cook or freeze your tank individually. Together they are more than adequate to run your system. Also consider a Ranco temperature controller in the future.
Powerhead - You can spend a lot or a little. You can get some that are capable of creating wave patterns or some that just move water. I would recommend at least two in your tank. The Koralia 2 or Koralia 3 would be cool and very affordable.
Salt - the biggest debate in reefing on the planet. Instant Ocean is widely accepted. Pick one that you can find locally. Buy the bucket for whichever you decide on. It will contain enough to mix from 150g to 200g of saltwater. You'll need it for regular water changes.
Refractometer- Don't cheap out here by buying a hydrometer. This is one of the most important measurements you'll need to monitor. A refractometer is infinitely more reliable. No matter what size tank you start with, please don't start with a hydrometer. As a matter of fact, the smaller the tank the more important it is to use a refractometer.
Test kits - Salifert makes the best affordable and efficient test kits for the hobby. You'll need ammonia, nitrites, nitrates, pH, calcium, alkalinity/hardness, magnesium. Any more than this is not really necessary but available if you want them.
RO/DI water filter - Your tap water contains loads of TDS (Total Dissolved Solids) that are prime for causing algae outbreaks. If you get a TDS meter you'll be able to test your tap water. Mine comes out of the tap at 105 ppm. We want zero. 'Nuff said.
Lighting - I could write an entire book on reef lighting. Depends upon what animals you want to keep. Metal halide, T5, Powercompact (PC), LED, combination of MH & T5 or MH & PC is a great combination.
Thermometer - The Pinpoint Wireless thermometer is very reliable.
Return pump - Depending upon the amount of vertical height you're pumping your return water will determine the size pump you need. Remember, as water is pushed up vertically, as well as the friction of the pipe it is flowing through as well as the # of fittings (elbows, unions, ball valves, etc) will reduce the flow you get through the discharge in the tank. A 1" pvc pipe overflow can handle NO MORE THAN 600 gph. Therefore, you might need a 1000 gph pump to compensate for vertical height plus backpressure from the fittings used.
Marineland Utility Pumps are fantastic.
I can list more things you can use, fluidized media chamber for carbon or phosban, controllers for lights & heaters, monitors for ORP, pH, nitrates, phosphates, calcium reactor, nilsen reactor, and lots more.
Do yourself a favor and do not under any circumstance use a wet/dry filter with bioballs.
I didn't list any books, but this is a must for you.
Hope this helped,
swimmer
BTW - Welcome to MR
