Hey Seth! Oh boy, now we have two Seth's, this will be interesting. I hope you stick around long enough to be one of the regulars. Welcome to the site, and I hope you enjoy your stay.
With that being said, I know you are anxious to get started in the hobby and you have all good intentions. Now is the time to start researching. Buy/Rent a good book on the hobby. The Conscientious Marine Aquarist by Bob Fenner is a good read. There's quite a few others, but that one is the most basic. I also highly suggest to start reading the 101 tips for new hobbyists in the "New Hobbyist" section of the forum. That will give you a pretty good basis of understanding so you can ask more educated answers. There's also a wonderful "search" function at the top of the forum, which if you don't know something and you want to learn, do a quick search for it, because chances are someone else has ran into the same problem.
In regards to your current questions, a 55g is a perfect starter aquarium. It's not very deep, and doesn't allow much room to aquascape, but it's what many people start with. 100 pounds of live rock is a good and fair amount of rock, but in today's modern aquaria, it's a little overkill. You should be aiming for around 75 pounds of rock total, but you can divide that amount in half - 37.5# live rock and 37.5# base rock/dry rock. It will help out on your budget. Put the dry rock in the tank first after your dry aragonite sand and then put your live rock on top of the base rock. Base rock will be seeded with bacteria, algaes, sponges, and all manner of sea life in the on coming months, essentially becoming live rock for half the cost. I know a decent place that you can get 40# of live rock for about $140 with free shipping. That's about $3.5/pound.
The canister filter isn't needed. In fact, many saltwater aquarists try to avoid canister filters if possible because the habit of them producing more nitrate/phosphate then they remove. There's also issues with monthly cleaning and saltwater creep/leaks. If you are looking into getting a new filter, I highly suggest getting an Emperor 400 biowheel filter. Some people here (Flower) will come and say that it's the most horrible filter there is and there is salt creep everywhere and yadda yadda, but I think that is BS, because I've used them, very effectively, for years.
Not only will you have to have a new filter, but I also suggest looking into an efficient skimmer. Stay away from the dreaded Seaclone and Coralife skimmers - Usually a beginner hobbyists first mistake. (though, Coralife does half way skim correctly, many people have reported issues with leakage, and the way the skimmate cup has to be removed) If you get a protein skimmer, I suggest investing a little extra money into one that we all know is going to work. Octopus hang on back skimmers do very well. Eshopps is great if you are on a budget, and many others have reported good results with Remora skimmers. Skimmers remove built up dissolved organic and particulate organic matter in the water column that can cause nitrates and phosphates to increase. So, overall, they are a good thing. There are more natural ways of waste removal like algae scrubbers and macroalgae, but for a new hobbyist, a protein skimmer is a good investment.
There is also two other pieces of equipment that you will have to invest in. One of which is a heater. fully submersible titanium grounded heaters are a great investment. I suggest buying two smaller heaters to put on either side of the tank for even heating. But, one larger heater is fine. All heaters can easily add stray voltage to the tank, so put your aquarium on a GFCI power outlet, and use powersupplys with a built in fuse. Also, it's a good idea to use a titanium grounding probe to direct stray voltage out of your tank.
The other piece of equipment that you will need, and arguably the most important, is powerheads. The standard powerhead to use in modern aquaria is a Koralia style powerhead. Koralia is a brand name, of course, but I use Koralia powerheads because they provide a much wider water stream which stirs up more detritus and waste than a standard powerhead. You should aim for 20x to 30x your tanks volume in powerhead turnover gph. So, for a 55g tank, you are looking at a minimum of 1,100gph coming from your powerheads. I suggest getting a minimum of two powerheads, rated for 550-700gph each. That will put you at about the right flow rate.
There's a lot to learn to get started. I see that you want a reef tank, so I highly suggest getting only reef safe fish. Stay away from damsels by all means. Damsels are small, but they can be little devils - terrors of a tank. Read and research every purchase before you buy it, this includes equipment AND livestock. Remember, these are living creatures we take care of, not just ornaments or pretty looking things. It's up to you to try your best to provide an environment that will suit them, to make them healthy and grow.
If you need any help one on one, don't be afraid to PM me or e-mail me. I'll be happy to help you along the way.
