What was your first experience in game dev communities?
My first experience with communities was Game Jolt for a couple of months, then I moved here to itch.io. A game dev community is something that I'm very proud to be a part of and I've gained lots of wisdom and knowledge from frequently making posts to the itch.io forums. If you have a problem, there are people willing to help who may have either had the same problem or straight up want to help you fix it. I've also asked some people to share their feedback with one of my older games which steered me in the right direction and helped me a lot.
Is it okay to share unfinished, or even just started, showcases and projects?
Whatever the project's state may be, whatever you feel comfortable with, you should do. I'm working on a new game that I haven't even written a line of code for, it's still just an idea. But one thing I do not recommend doing, is releasing an unfinished, rushed game. You should always take your time when making a game. As I always say, quality > quantity. But if you have an idea you're passionate about and want to make into a game, share it! People will provide feedback, or maybe even changes to make it the best idea possible!
How should I go about finding people who might be interested to work with me who have different skills, such as artists?
There are literally thousands of people on itch.io alone that are looking for jobs, especially artists. The best/fastest place to find a worker or someone to help you is on Discord. There are hundreds of game dev servers on Discord. I'm in dozens of game dev servers myself, and if I run into a problem, I've found someone who helped me fix it right away. It's very rare that you don't find someone, and anyone can at any price. Sometime people will work for free!
Would it make sense to record "making of" my first games, and share on Tubes? Is it wasted effort until I get a better grip on the whole process, or can it help prepare for a possible launch?
I can only imagine you're talking about posting dev logs to YouTube, and if you're passionate about it, then you should do it! It takes time, and it's a fun little side project. It can also lead to more people finding your channel and it can build up some hype and get more sales! It's a very efficient marketing method. Tons of devs do it! Big and small.
I wish you luck on your game dev adventures! I'm 16 and I just started making some games of my own. :)