That's great!
3cm depth is normal and fine, and will work for most plants.
You absolutely can, but you also don't need to wait until it's completed! Tanks are constantly evolving anyway, they're never "finished", if you know what I mean? And people are more than welcome to enter tanks even if it's a build in progress and you haven't got to where you want it yet. We've even had an empty tank with decor, a stunning daphnia colony bottle, and a lovely planted container only containing snails entered before! Right,
@Fishmanic ?
You'd be more than welcome to enter any of your current tanks or builds in progress, explaining your plans, when they're the right size tank for that month, and you should! It's just for fun, a social forum thing, a great way to learn, interact on the forum, and share your aquariums and plans.
It's not a hardcore competition, so if you enter without worrying about whether you'll win or not, because even if you don't win, there's always next time! I've entered loads of times just for fun, even knowing there was no way I'd win, just because there hadn't been many entries, and it encourages others to join in too.
So I entered many times just for fun, worked on one tank to get it looking as good as possible, took several photos until I found one I liked, and it was a nice surprise when I did win once! Then you get a banner under your name. You can also enter the fish of the month and pet of the month contests if you have other animals.
It absolutely is! There's a lot of misinformation on the internet too, so always worth checking the source. For precise and accurate info on most any species of fish,
Seriously Fish has profiles on most any species of fish you're likely to come across in the hobby, and it's written by scientists and experts in the hobby, so you can rely on the information there, compared to random blogs or pages when you do a random Google search. You can look up any species you want, or have, and see what requirements they have, and can check if they'll be suitable for your current set ups, or if they'd need a larger tank, or different temp range, or wouldn't mix well with your current fish, info like that.
Like, what fish do you have at the moment? As an example to show you, here's some profiles for some species of fish I keep. I searched "Seriously Fish bronze corydora" since that's the common name you see in the shops. It brings up this profile, which also gives you the species Latin name, since some species have different or shared common names, but the latin name is specific to each species and sub-type.
Bronze Corydoras are common in the hobby, as is an albino mutation; albino Corydoras may be albino versions of
Corydoras aeneus (bronze cories), or they may be albino
Corydoras paleatus (peppered Corydoras), or even albino versions of
Corydoras sterbai! All three species are common in the hobby and available in most stores, but have some slightly different requirements. By looking them up on Seriously Fish, I was able to learn I could keep my Bronze and Sterbai Corydoras together, since they both tolerate harder water and are in my range for GH, but peppered cories (
Corydoras paleatus) need a cooler temp than the others do, so I don't currently have that species.
www.seriouslyfish.com
www.seriouslyfish.com
www.seriouslyfish.com
So this is just an example of how important it is to have reliable info on species, especially before buying them, if possible! By reading the profile you learn the latin name, where they originate from and the habitats they need - especially important when you're setting up a tank or you're into biotopes. You also learn how large the fish can get at adult size (some fish sold in stores like bala sharks, common plecos and many loaches can get absolutely massive and need monster sized tanks or ponds once they get to adult size, and people buy them as cute babies, without realising how huge they will get, then either stunt the fish by keeping it in too small a tank, wind up with incompatible fish that fight and kill each other, or have a hard time rehoming them).
The Seriously Fish profile will also tell you what maintenance they need, what water conditions ranges they can live in, like the temperature range, pH, and water hardness. What diet they need, typical behaviour and compatibility (i.e: if they're a social fish that needs a group of the same species, or show aggression to tank mates and do or don't suit community tanks, etc), and even how to breed that species. So it's a really valuable and reliable resource, worth bookmarking!
You are! We all are. We're all still learning and adapting as we learn more, and there's so much to learn in this hobby, and things do go wrong occasionally in this hobby. It's inevitable, and you're never alone there. No matter how long someone has been in the hobby, how hard they try, how experienced and knowledgeable they are, things still do go wrong now and then. Equipment can fail, tanks can fail, we're only human and make mistakes, or we follow advice that turned out to be wrong, but we were doing the best we could at the time, with what we know.
No one expects you to be perfect, I promise.
We like to help, it's what the forum is for! So don't be afraid to admit to mistakes or ask for advice. Some places like some groups on Facebook or Reddit can have members who are harsh on beginners or people who make mistakes, and then drive people out of the hobby, but that isn't the culture here.
Here we want to help people, share and learn from each other, and help each other out so we all do better in our hobby, and can share our passion for the various areas of fishkeeping. If anyone is mean or breaks the rules, the mods are great here, just report the comment and let the mods handle it, but don't let it get to you. Take the advice that you find helpful and works for you, and leave the rest.
We also all have good and bad days, and tone is hard to read by text. I know I've been too harsh on others at times when going through a rough time personally, then apologised and fortunately been forgiven when it's happened. We're all only human! But in general, most people here are lovely and helpful, want to help where they can, and people who break rules are handled well by the mods.
Wet Web Media is another really great, reliable source of info I often recommend checking out and bookmarking. Also written by known experts in the hobby, they can give advice if you write in, and it's always worth doing a search on their site if you're having a problem, since you can read their answers to previous questions about the same thing, and learn a lot that way. I've spend many hours reading advice there when I had an illness in my tanks, if I had a sick fish, things like that. I also emailed them and sent photos when I thought my otocinclus was carrying eggs, and got some lovely, helpful and quick responses from one of the experts there, Neal Monks.
So those two sites, and here of course, are places I recommend for learning more! Can also use the search feature here to find previous posts and threads on any topic or problem, or make your own thread if you want more personal or specific advice, or want to make a journal thread if you want to do a build/journal thread about a specific tank you own. Those are great fun, and people can be really helpful and supportive!
Exactly! We all make mistakes. I guarantee, there isn't a fish keeper in the hobby who hasn't made a mistake at some point. There's so much to learn in this hobby, and the learning curve at the beginning is steep, with a lot of misinformation online and from fish store employees even, so no one expects perfection, any mistake you make, you won't be the first one to make it, and others will want to help, as we are trying to here!
You've already said the most important thing, and you're absolutely right. The important thing is how you work to learn from mistakes, and improve from there! That's the key, and it's why you can succeed in and enjoy this hobby, and participate and benefit from this forum, I hadn't been participating in threads much recently, I tend to dip in and out depending on how busy real life is, but here's a belated welcome to the forum from me anyway!
Never have to get a mouthful of tank water and microcritters again! 
