Your characters look awesome! I want to make my own as well (I'm not going to post my terrible looking characters). From what I've read in my research... Making the outline of the story is key (like writing a book), then story boards, then actual fleshing out of the manga itself. I'm doing mine by hand. (because I don't have any computer art skills) I don't plan on publishing mine so I didn't do any research on that aspect. There are some good YouTube channels that cover a lot on making a manga. Yuuike, My Mangaka LIFE, and Artfinitii, to name a few. I don't know if that was any help. Best of luck!