@DonpomOh by all means, two-dimensional characters have their place and I have used many, many of them as NPCs for the RP plots that I run- but the thing is as you said, that is the limit. It seems like a waste to spend the time to make a PC you know will not last and that may be excellent in certain scenarios but will otherwise limit you to where you can reasonably RP and what you can reasonably do.
When it comes to things you don't know, the internet is your friend-- though as is imagination and a touch of improvisation. One of the characters I play is a character that is a respectably high ranking Garlean doctor, essentially that focuses largely on magitek prosthesis and augmentation. Before I started playing I had a little bit of an idea from medical training, though most of it? Google. Researching and learning more so I could not only figure out ways to do certain things but use it as inspiration to play with ideas and concepts that simply do not exist in the real world. Have fun with it! There were so many times in RP I ended up either looking something up in the middle of a post I was writing or just going "Screw it, we'll do it live!" It's created aspects of my character that I never thought of before. Plus, you can learn some really interesting things in general.
When it comes to the 'jokester' characters they can be fun but I'm not sure if that should be your main focus for it. Don't make it the base, but figure out a way for it to mesh onto the side of what you already have. How old is he? What does he do? Why does he struggle to cope otherwise/what brought him to find that comedy was an effective way to play it off? I'll use my character above, Adlai, as an example as he can sometimes deal with things similarly:
How old is he? He's 30. Why is it relevant? Because while he's seen a lot of things there is a whole lot more and he hasn't had the years behind him to help give him a wiser view and help him deal with such things.
What does he do? He's the head of the medical side of a castrum. Why is this relevant? Because he has a stressful job looking after and developing new things while having to ensure the wellbeing of himself, his staff and his patients.
Why does he struggle to cope otherwise? His nerves were shot from previous events and are overall an incredible anxious creature. Why is this relevant? When he doesn't have to be professional and serious it is easier to use comedy to write off something, distract from it or otherwise dissipate the tension.
This is of course only the most basic of things to begin with for example's sake. It's all just a very tiny part of him. It's like a bonus feature that makes things more interesting but wouldn't destroy what my character what without it. I guess that's really what I'm going for here. If that is the only thing going for a character and it would fall apart without it? It's best to place it aside and then add it later when it has something to truly mix with.
In regards to my second post, I feel that while they may have been wanting to tell a good story, it excludes those who are interacting with them at the time. If they wanted to tell those around them ICly what they did then by all means do so and give the characters a chance to listen and respond. Storytelling is a wonderful thing and it's something that we all do simply by RPing, but make it with the characters that yours is interacting with rather than despite them.
Finally, what @Aegir said is pretty much spot on-- and having that variance and balance in plots types is incredibly important. Not having that flexibility can easily kill a plot or a group idea.