Wait until you've been in the hobby for awhile. The contradictory and various opinions on issues just keep on getting funnier...and more numerous...lol.
I think it's because each and every system is very individual and what might work for one person may not always work for another. Here are some simple guide lines to follow...
The larger the tank, the easier it is to keep good water quality. Hex shaped tanks don't have much room for healthy gasous exchanges between water and atmosphere. So rectangular tanks are more beneficial for having a larger surface area for these gasous exchanges. Also, rectangular tanks give the fish more room to swim and gives more room for available territory (allowing you to have more critters without them ripping each other apart for space).
Choosing between a glass tank and an acrylic depends on what you plan on putting together and what you can afford. If the tank is going to have a lot of rock work, you'll be better off with glass. Acrylics scratch real easy. They also cost more than glass and may warp over time. Another downfall to acrylics are the openings at the top. There's very little room for anything.
Filtration is easy, though the kind of filter depends on what you plan on having. Is this going to be a reef tank? Fish only tank? FOwLR
? In any of these situations, you will want to have a protein skimmer or refugium. If this is going to be a reef tank, then all you really need is a protein skimmer or a refugium. No additional filtration needed. If other than a reef, an appropriate size canister or HOB
filter in addition to the skimmer or refugium would do just fine. Under any and all circumstances...avoid undergravel filters.
I do suggest reading about deep sand beds (DBS) and how they can help control nitrates. This can be very useful in a tank with lots of rock work. DSB
can eliminate the need for vacuuming the substrate for solid waste, though partial water changes will still need to be done routinely as well as maintaining the filter.
What ever questions you have, always ask...and keep on reading.