Just a few rambling thoughts.
First, boiling rocks exploding -- until someone shows some proof -- I call myth. Break - maybe. BAKING rocks with dry heat I might believe, as some people do that in ovens. Steaming rocks - maybe bad idea for same reason, because baking and steaming can raise the temperature of the rock WAY above boiling. I still would have trouble thinking it could really explode but it's at least plausible.
But BOILING a rock means the temperature of the water it is boiling in is at 212F (sea level and clean water). It cannot get above 212F. The rock is going to VERY slowly (because that's the nature of rocks) come to 212F, and even if it had a nice sealed pocket of water inside it's very unlikely the water is clean enough to boil at 212F, more likely it has salts of various sorts that will keep it from boiling. And the bath it is in cannot get hotter than 212F. In fact most people who "boil" rocks or driftwood do so at a slow simmer, which if you measure it is probably about 190F.
Be safe if it makes you feel better and don't boil them, but I'd really like to see someone who is so strident about the warnings offer some evidence it really happens as opposed to a continued myth?
Anyway... rambling to the OP's question...
If I could do one thing different I'd just have stopped, and done a lot more reading and thinking and looking and research first. Practically everything I bought initially (except a pricey heater someone talked me into, and an API test kit same thing) was junk.
I went through two HOB filters being told they were quiet -- they weren't.
I rushed to put fish in -- I should not have, I should have done a fishless cycle.
I didn't have a clue how to do planted and thought I could decide that later -- you can't really. If you want a planted tank you really need to start that way first. Which means you need to decide what kind of planted tank - high tech, low, low light, etc. Lights now you need to think about LED vs Florescent.
If you just buy a tank with "LED lights" at a sale, it won't do plants (probably). That's great if you don't want to do plants, but it means it's trash if you do.
It doesn't really sink in for a lot of people that bigger really is EASIER for a fish tank, within reason. So long as you can manage the water changes OK, bigger is more stable. Always.
It's practically impossible to figure all this out without actually going through it and buying something and making the mistakes, but you can read and talk to people and avoid a bunch of them.
For example -- think about where you are putting the tank, and work mentally through how you are going to change water. Do you have a path for buckets or hoses to where you plan to get it from? To get it out to discard?
Do you have a way to get the water at or near tank temperature?
Or more basic -- do you want salt water or fresh (HUGE differences in what you need to do there).
Do you want a peaceful community tank, or something with more aggressive (and oddly that often means more beautiful) fish. Some fish, for example, you only want rock in the tank; some plants or decorations are good. Some need caves, some don't.
One good approach is see if there's an aquarium club nearby, often that has lots of people who are interested and love to talk about what they have/do, and will share what they learned.
In general don't listen to anyone at a chain pet store. Sometimes they are knowledgeable, more often they are filled with rote stories and info that's more wrong than right. At the very least take what they recommend and go verify it online after the fact.
Perhaps the biggest thing you need to obtain is a HUGE dose of patience. Most things take time - cycling the tank is just the first. If you rush and buy stuff, you will just end up replacing it, all too often. If you can get the right size tank, that's one semi-exception, as a tank just holds water. It's all the other stuff that has too many choices. But even a tank can be an issue -- tall tanks for example are not as easy to keep as planted tanks as shallow tanks.
Sorry for a long ramble.... hope it at least makes you think...
