Well, you are starting out with one thing few new aquarists have, patience. It shows great wisdom to research any new endeavor.
A 55g tank is one of the two best "starter" tanks in my opinion. The other is the venerable 29g. Both are great, in that they allow the beginner a larger tank to begin the maturation process into the hobby. So many start a tank and want one of every fish they see in the local fish store. This just doesn't work, needless to say. With either of these two tanks, you are capable of putting together a unique and beautiful biotope that you will enjoy and your fish will thrive. Many start with a 10g tank. This tank is small and maintainence heavy. The larger tank allows you to make a few mistakes and have your fish survive your faux pas.
You must first decide on the one single fish you must have and build around the requirements of that fish. Decide on the theme for your tank. Examples would be Rift Lake Cichlids, Amazon Backwaters, Amazon Riverine Fish, Western African Rivers, South American Dwarf Cichlids, Blackwater Biotope, ect. You then select the fish that are endmic to the theme. You will be able to select other non-endemic fish that will thrive in similar conditions, if you like.
For example, if you were to choose "blackwater Biotope" as the theme for your tank, you would have driftwood, plants, a few rocks and fish such as tetras, dwarf South American cichlids, angel fish, discus, wood cats, farowellas, corie cats, ect. Now some of these fish would not be for the 29g or the 55g as they grow too large upon maturing, but this is to give you an idea of what can be done. Water would be soft and colored by taninins from the wood. The water would actually have a "golden" color.
If I had to choose the biggest mistake by the beginning aquarist, it would be the lack of patience when setting up a tank. It takes a tank anywhere from 2-12 weeks to cycle and get its bio-bed up, running and healthy. Please exercise patience during this initial phase of actually setting up the tank. The second is probably either overstocking the tank or mixing incompatible species. Both are bad and can ruin the perspective of the novice.
The biggest problem after all is set up and fish are added is lack of maintainence. Weekly water changes are mandatory. Sometimes, you may have to perform these duties more often. A minimum of 25% water re[lacement is recomended, sometimes 50%, depending upon the species of fish you are keeping.
As far as filtration, I believe more is better. Some use the rule of thumb that the water in the tank should be "turned over" 4x-5x per hour. I have tanks that are filtered over 30x per hour. Most are filtered 15x-20x per hour. This must be accomplished, in most cases, without undue current in the tank. Not an easy task. There are also a myriad of filtration systems on the market. Never rely on a single system. Most of my tanks use a combination of filtration systems, underground filters(ugf's), power filters, canister filters, powered sponge filters, sponge filters(air driven).... As you can see, the choices are large.
Lighting is a very debatable subject. The old "watts per gallon" addage is archaic and misleading. Depending upon the requirements of the inhabitiants, including plants, you will need to provide sufficient lighting, both in intensity and in hue.
I hope that I didn't scare you off or confuse you. This is just some of the things you will need to research and take to heart. Good luck and welcome to the forum.