Skriz;373495 wrote: There's a lot of bad advice here, so let's go over a few things:
Sump-get the largest sump you can fit/afford. A commercially built sump will offer you the ease of simply purchasing it. It will also be correctly designed and built for best performance. You can build something yourself, but you'll have to decide what you are wanting to accomplish with the sump and which materials you are confident with working with. The easiest diy sump would be a rubbermaid container; not the prettiest, but it does work. If you've never worked with acrylic before, I wouldn't build a sump as your first project; it's just not worth the risk.
Skimmer-there isn't a better and more easy way of nutrient export than a good protein skimmer. The above advice of going skimmerless would only apply if you are planning on massive water changes, or you're planning on buying the crappiest skimmers on the market (some are just not worth wasting your money on). A good qaulity skimmer is worth it's weight in gold; it will make your tank more enjoyable as you'll have to do less work to keep the water clean.
Your life support system on the aquarium is going to be the single most important component; it is what keeps your fish and corals happy.
Books and test kits. Take your time and get some good books. Not only are they good reading, but they will really teach you a lot about the jounrney you are about to embark on. There's a TON of information out there and even more misinformation; good books will give you a solid foundation that will help you determine which info is what.
The number one thing to get right now is PATIENCE. Nothing good comes from rushing into things with this hobby. The number 2 thing to get is an ARC membership