I'm making a comic so a good deal of planning is necessary - I can't go back and change things very easily. That would be the case even if it weren't a webcomic. Releasing parts of it while other parts are still being made only makes that worse! So yes, I'd recommend some degree of planning.
That said, you don't need to write the WHOLE thing. I have the script written for most of the opening act. There are still some gaps, but I have a good idea what I'm going to fill them with. There's enough content here for the whole first year of Blue Star Rebellion, at my current rate, so I don't have to worry much about running out of script.
Beyond the first act, I know the overall plot beats of the first major mission. I have little scenarios and bits of script written down. They're still puzzle pieces, not yet a unified whole, but I know what the picture looks like.
After that mission, there's another two which are way more hazy, beyond a general 'x happens, and they have to go do y'. Those stories are ages away, though, and all I need to know is the general shape of them in order to start building themes and foreshadowing toward them.
So, plot-wise, I've got some planning, but not everything. As for the characters and worldbuilding though, they're absolutely planned out. I've been working on them in some way, shape or form for a decade. I wouldn't start writing a character without having any idea what they were like unless it was a first draft and I knew my decisions weren't set in stone. If you're writing a story and releasing it to the public as you go, know your characters well before you start to share. They will still surprise you as you write - they always do - but if you know them well, hopefully you won't have to go back and re-write major chunks of the story in order to keep their behaviour and values consistent! Same with the worldbuilding.