Your very first ever webcomic? Congrats! Here's my advice
Start drawing.
Don't overthink it, the most important part is to *make the comic*. It's very, very easy to "feel" productive (tons of plot notes, character doodles, reading/watching videos on how to thumbnail comics, you start writing the script, maybe even get to sketching a few pages) and then it fizzles because you're so overwhelmed and perfectionism takes over. You can ALWAYS go back and re-draw stuff you don't like, later.
Fact is, you'll learn most of that stuff as the comic progresses anyway. "Make it exist first, you can make it good later"