It's true that bigger is sometimes better, yes. It of course allows more room for error. At the same time, you tend to spend more initially to set up as well. Personally I would say that from a begginers standpoint, go for something thats 20 Gallons or more. Having had a Freshwater 10G, things can change over the course of a matter of hours or less. Now having something that is 4 times larger, and being saltwater (having to deal with more parameters as well), It seems like things take a LOT longer in itself to actually start to change. This in turn, gives you more time to act on these changes and make the appropriate corrections (ie: water changes, phosphate removers, adding suppliments, etc.).
The size you're looking at of course has pro's and con's just like any other size tank. The fact that your tank will cost less to set up because its a "package" is of course a benefit. You'll use less salt, water, chemicals, Live Rock, Live Sand, and buy less livestock in order to fill this tank. On the other hand, having a tank that is comparably smaller, you'll end up with less room for error, less choices for livestock (no tangs), less ability to keep everything you want, etc.
Having a bigger tank, you get more choices in fish (you can have tangs), more room for error, the ability to keep a bigger range of species because of the added room, you get to keep more fish in numbers, etc. Its not to say that going bigger doesn't have its faults either. With a bigger tank, you have to spend more initially, use more salt for water changes, more water for water changes, there isn't really anything in terms of a "package" for larger tanks, added weight on your floor, more space in your house being taken up by this tank, etc. Equipment is much more expensive as well. You need to buy the more high end lighting equipment because most bigger tanks are taller as well, meaning you're going to need more watts/gallon to keep some of the higher end corals too. The skimmer will need to be bigger/handle more, the list goes on.
I'm not trying to bash either one, heaven knows deep down I want a 400G tank someday, and at the same time, I'd love to keep a tank that's 9 Gallons or less. This hobby is so fascinating because of the challenges that we as reefers have to deal with. Things like mixing and dosing chemicals to add, setting up the Live Rock just the way we want it, picking and obtaining the fish that we want, battling disease, changing water, and much much more, it's never ending. But, in the end, there is absolutely nothing like sitting down in front of your tank at the end of your day, and just watching the little bucket of the ocean you have created.
