It's not that complicated. First, you need to scan the paper comic pages and digitize them. Then, use graphic design software to optimize the images for web display.
Most web comics nowadays aren't made with Flash. Artists have a wide range of options like specialized comic drawing software or even hand-drawn and digitized methods. Flash has become less popular due to its limitations and the availability of more advanced tools.
To make web comics, start by coming up with a unique concept. Then, work on character designs that are appealing and distinct. Also, pay attention to the composition and flow of each panel for a smooth reading experience.
Well, formatting comics for the web involves several things. You need to optimize image sizes for quick loading, use a consistent style throughout, and maybe add some interactive elements for a better user experience. Oh, and don't forget about making it mobile-friendly!
It's hard to give an exact number because new web comics are constantly being created and some may go offline. But there are thousands, if not millions, out there.