Its a wise and lucky choice to begin your research early, without even owning any equipment yet! You are correct that there is an advantage to having a tank of fairly large size for a beginner. Larger water volumes are more forgiving. They can't change water parameters as fast and thus give beginners more time to recognize and react to a problem. This is true of course, only up to a point (debatable what size that point is.. 75G?) because past this point the labor of maintenance builds "beyond easy" and other problems can creep in, such as too much depth for your reach.. other odd things like that.
By planning prior to owning, you can discuss pros and cons of actual tanks and all the bits of equipment. There are members who will have a feel for some of the more important things to watch out for in those larger tanks and how they should be equiped.
My own feeling is that for the beginner, filtration is perhaps the most core topic to give learning priority to, as it will be important right away even if you can't get all the other things resolved. In the tank volume range you are considering, people often employ two larger external cannister filters, which has the nice effect of maintaining stability with one filter when the other has been cleaned on an alternating schedule.
The three main filter functions are mechanical filtration, chemical filtration and biological filtration. Mechanical filtration is the obvious one that is all most beginners think is going on at all. The water is forced through smaller and smaller places until more and smaller particles are trapped and can't return to the tank. Tightness of fit and correct placement and media order are important considerations for mechanical filtration and it is the most dependent on the expertise of the filter designer.
Chemical and biological filtration are both often misunderstood. Chemical filtration is most commonly optional and dependent on individual situations. We usually recommend that beginners here at TFF do not use chemical filtration unless they've discussed it here and the members feel it would be useful. Carbon (aka activiated charcoal) is a common chemical filtration media and is useful most often for three specific things: removing medications, removing tannins (yellow tea-stain effect from bogwood etc.) and removal of organic odors in special cases. Carbon adsorbs these things for about 3 days only and then is ready for removal and trashing. So carbon is good on your shelf, but not on a regular basis in your filter.
Biological filtration is the most important and one of the most fascinating and unusual aspects of the hobby. This is the bit of science that can take even old-timer fish hobbyists by surprise. As it starts out, a filter with media has an initial mechanical capability but is really just raw hardware and not fully functional in the hobbyist sense. What's required is some knowledge and skill that's been clarified and improved in recent years. It turns out that two specific bacterial species must be coaxed to grow in the filter and these two types of bacteria will form a working biofilter that chemically transforms the tank water.
Fish not only give off CO2, like other animals, when they respire, they also give off a significant amount of ammonia, directly from their gills! This, combined with fish waste, excess food and plant debris will combine to pollute the tank with ammonia in very short order. After conditioning, there will quickly be millions of heterotrophic bacteria in the water which will rapidly perform the conversion of the animal and plant debris and the excess food into ammonia. Ammonia, constantly washed away in the huge water volumes of nature, is a deadly poison when it hangs around and causes permanent gill damage and death in relatively small amounts.
The first bacteria we grow (we'll call them ammonia oxidizing bacteria or "A-Bacs" for short) are an odd species that cling to surfaces and live where there is abundant flow of oxygen and ammonia and they "eat" and convert that ammonia to a different compound called nitrite(NO2) which is released back to the water. The A-Bacs are not heterotrophs, they are an example of a group called chemolithoautotrophs (literally "Eaters of Rock" because, as autotrophs, they don't eat other organic things like the rest of us animals, instead they literally are the beginning of the natural cycles that help convert "Rock", calcium for instance, into more organic things.)
Unfortunately for us, nitrite(NO2) is -also- a deadly poison to fish, as it "suffocates" their cells by means of displacing oxygen from its important positioning on the fish blood hemoglobin molecules. The first cells to suffer are the nervous system cells and even small amounts of NO2 will cause permanent nerve damage to fish, often not very detectable from outer symptoms at first.
This is where the second bacterial species we grow comes in to save the day. The second species are nitrogen oxidizing bacteria (we often call the "N-Bacs" for short here in the "New to the Hobby" section on TFF) which "eat" the NO2 and covert it into nitrate(NO3), which is not a particularly nice thing to have in your tank but is relatively harmless compared to the previous two substances and thus we can let it hang around until we perform our weekly water change, which will dilute it.
So this thing called "Fishless Cycling", which the members and the pinned articles are going to tell you all about is the new method devised in the 1980's and improved over and over to grow these two species in the filter and be sure you have a working biofilter prior to the introduction of any fish. The two species form "biofilms", sticky films on any surface they can attach to, which, as it turns out, also help to put the final touch of effectiveness on the -mechanical- media, by making it stickier and thus better at trapping particles of all sorts. But the main bio function is the most important, effecting the amazing and rapid transformation of ammonia and nitrite(NO2) into the more harmless nitrate(NO3) and doing this on a constant basis, hour after hour while you go about your life away from the tank.
Sorry.. know this is the "long version" of a story but perhaps you'll turn back to it for some of your questions, so enjoy!
~~waterdrop~~
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