Hi Mike,
It sounds like you've got things going good so far.
As this is your first sw tank - you selecting a 72 gallon tank is a wise decision in my opinion.
You mentioned that you've read about the nitrogen cycle - so you're ahead of many folks just starting out.
Here's just a few basic things I found helpful, that I learned either here on the board or from reading, that allowed me to avoid some of the common problems I encountered during the first year on my first tank.
Everything begins with the freshwater.
Use good quality freshwater - either RO, DI or RO/DI.
Tapwater can be used - but you may risk having excessive nitrate or phosphate problems down the road. It all depends on YOUR tapwater.
You can easily avoid many future headaches and problems by investing in an RO or RO/DI home unit early in the game. Other equipment toys are nice to have - good freshwater is so important that I don't consider the RO/DI a toy, but rather a valuable tool. It took me a year to figure that out.
Many people choose to buy RO or RO/DI for their freshwater source. This of course is another good option.
Water circulation. Not only do you want good quality tankwater - you want to make sure it's moving around in the tank pretty good.
Slow moving dead water is a sure fire way to lose creatures, does not get the waste/detritus up for it to be filtered/removed, and can cause gas exchange problems. Water chemistry and fish/inverts health and well being is affected by the movement and circulation of the tank's water.
I didn't notice any powerheads listed on your list of stuff.
Even though the powerfilter and skimmer will help, you may want to consider 2 or more powerheads. More water circulation is often better than too little.
Get some decent test kits and begin a routine of using them. After a few months - some of the tests are not required near as often.
Even though you have a decent sized tank - don't be tempted to stock it too fast with fish. Rarely do you hear of a new tank having problems from stocking slowly, with months between new fish additions. It's the too many too fast that can jump up and bite you.
Expect some brownish/rusty colored diatom growth around the 3-6 week old timeframe. It's common - it likely will go away in most every case.
Expect some other algae growth as well - but realize that a little algae in the tank is considered a good sign by many. If you see large areas becoming overgrown with heavy algae growth - you may need to takes other steps.
After your cycle - watch the nitrates and phosphates with test kits. In most every case, these kits results will tell the story "before" you actually see the problem appear.
In other words - you can somewhat "predict" what may happen later if you know your tankwater conditions before.
After making sure you have great freshwater for saltmixes and evaporation top offs - I'd say that having a lot of live rock in the tank is probably one of the best insurance policies you can have for success. It's just great stuff - looks cool - makes the tank look more natural - and provides excellent biofiltration.
A tank loaded down with good quality live rock, along with using good freshwater, and having a routine of doing some partial water changes - makes for a very forgiving system.
Not only for people just starting out in the hobby, but also for the more seasoned/experienced hobbyests with established mature tanks.
As you begin to think about fish/invert selection - try to imagine what you want your tank to be like say 6 months, a year and several years from now. Sort of have a visual plan on it's appearance, as well any plans to add corals or inverts.
The compatibility and disease/health risks of each fish/invert should be considered, as well as each creatures diet, swimming room, potential conflicts, special lighting requirements and how they may affect your future plans for each and every addition afterwards. What you add today may prevent you from adding something you really want later on ..... and vice versa.
Avoid the tempation to try all these cool looking marine tank additives you see at the local fish store or online. Although some established mature tanks that contain certain species of inverts or corals do have certain requirements for additional supplements - newly set up tanks rarely do.
Water changes with good water and salt - will do the trick for quite a while. About the only things I think you'll want to start reading up on is the relationship between pH, alkalkinity and calcium. It is by far the most difficult to understand for most, including myself, but after you get a hold of it, it will help you all along in the hobby.
I'll say this twice okay. DON'T OVERFEED ..... DON'T OVERFEED.
More problems with tankwater chemistry/algae growth arise from overfeeding than most any other thing we do.
Again, this is a sure fire way to booger up you tankwater.
And this last suggestions is directly from my experience, as I'm sure others would agree from their own personal experiences.
Ask or read - don't guess.
I've "guessed" wrong several times before - and had to deal with each set of resulting consequences.
Avoid before, rather than overcome after
