My fish info has been collected from all over, a great deal of it recently from browsing this forum, previously from books, magazines and knowledgeable local fish store types (all pre- internet, it's much easier now.) Most of your questions starting out can be answered by pinned topics on these forums,
http
/badmanstropicalfish.com/ has some great articles. For species specific information on my favorite fish, I like
Planet Catfish and
Loaches Online, most everything else except puffers I plug into google and read through as many articles as I can find, going with the largest minimum tank recommended and largest maximum size. The biggest trouble with most of the reliable fish info avaliable is that it reads like a science textbook, so hopefully you were/are a fan of biology and chemistry.
Sounds like it's time for the nitrogen cycle chat. Unless you're very lucky, the average local fish store employee doesn't seem to be capable of understanding it enough to explain it to every new fishowner that walks in the door, which is why you didn't hear it from them. Whenever someone on these forums refers to cycling a tank, they're referring to the nitrogen cycle as it applies to aquatic life, even though it sounds like it means that you should just run your tank empty for a week. The problem is, fish produce ammonia as waste, which is extremely toxic to fish. When you're cycling, preferably
fishless cycling, you're building up bacteria that break the ammonia down into less toxic substances. The first kind of bacteria to build up will convert ammonia to nitrites, the presence of nitrites will encourage a second kind to build up that will convert the nitrites to the least toxic nitrates. Regular water changes (10-20% weekly usually) keep nitrate levels down. All of these bacteria colonise your filter media (sponges, cartridges and such that are kept in your filter.)
The trouble with filling a tank with clean water and adding fish is that the bacteria haven't had time build up, so the ammonia builds up and kills the fish. Before someone had the bright idea to use household ammonia in their tank to get the cycle started, we all had to buy hardy fish, do frequent water changes every other day and pray that our fish didn't die. It's a bit of a pain doing your first cycle, but any tank after that can be "cloned" from an existing healthy tank by borrowing a bit of filter media and putting it in the new tank's filter at the same time as a few fish are added. Any fully cycled tank will have readings of zero for ammonia and nitrites at all times, if you haven't got a good liquid test kit (API does a good freshwater master kit) now would be a good time to get one. Make sure that you can test for ammonia, nitrites, nitrates and pH.
Once your tank is cycled (by fishless cycling or cloning from an existing healthy tank) you can start to add fish slowly, but not every kind of fish will do well in a newly cycled tank and no fish will do well in a cycling tank. The biggest problem with your angels right now is not that they'll get to big for your tank, but that young angels especially are extremely vulnerable in new tanks and yours hasn't even cycled yet, making matters even worse. I'd be shocked if any of your angels survive the cycling process. As for the gouramis, they tend to be much hardier than young angels but are still not very well suited to a brand new tank, I'd also be suprised if they survive the cycling process. You've also got too many gouramis for that tank, the males are very territorial fish and you've likely got two male dwarf gouramis unless one is extremely drab in color. If you do want to keep gouramis once you've got your cycle sorted out, either go for a single fish or a trio of one male with two females of a small species like the honey gourami. Your best bet right now would be to return them all ASAP, do daily ten percent water changes (with dechlorinated water of course) to keep ammonia down until then.
Filter media I can help you with a lot more if I know what sort of filter you have running on your tanks.