Welcome! 2 pieces of advice to hit your two questions:
Don't stress at all about this part! The secret to getting better is practice, and by doing a comic you'll practice a lot, so that'll come with time. The other cool thing about comics as a medium is that even if your art isn't like the most amazing thing ever, the story/writing can help carry the load! People will read an entertaining comic regardless of the art level.
I recommend starting with a short "one-shot" comic (or 2 or 3)! A one-shot is basically like short stories in writing. The length can be anything you want it to be, but like 1-50 pages is probably a good place to start. There are a few reasons starting with short stories is useful:
- Starting with a short project can help introduce you to the process of comic making in a "bite sized" fashion. It'll allow you to write out a whole story, script it, thumbnail it, and produce the pages, which gets harder and harder the longer the story is.
- It's easier to complete a short story without getting demotivated or burning out. Where a long, epic story might take years to complete, a one-shot should be complete-able in a few months to maybe 1 year. Creating a full story is really important so you get to have experience with every step of the process, and also just for that awesome feeling of completing a project.
Doing a few of these will give you a sense of how fast you work, and most importantly experience so you can plan your future endeavors better!
I guess the above mostly just applies to story driven comics though. If you're doing like a weekly strip style comic just hop in and get started xD
Best of luck and hope to continue seeing you around the forums!