You can technically post one chapter at a time, so long as the chapters are less than 15,000 words, because that's the word limit. So if your chapters are longer than that, consider chopping them up into parts. I think 15,000 words is a rather gracious amount for an application that's meant for "bite-sized" episodes vs. thesis-length amounts of texts. I mean, my chapters tend to run between 10,000 to 20,000 words on average.
Also, Tapas has stated that they are working on making image uploads a feature! (if I recall correctly lol) An ETA hasn't been stated as of yet, but hell, I'd be happy to hear it too if they can come up with a time frame (I'm honestly more interested to hear when they'll add formatting like italicizing, bolding, etc. .... because right now it's the bare bones equivalent of Notepad
)