I think you have a general understanding of what Tapas is and is not, but I'll go over it in case.
Tapas is a free online publishing service. It was originally set up for webcomics but expanded for online novels maybe three years back. It distributes your stories through its website, an Android app, and an iPhone app. It could not be more unlike Amazon which you pay to publish your books through its ebook and print-on-demand service.
Tapas is NOT a traditional publisher. It does not print onto paper and offers you no such option. It does not promote your work (99% true), and it has no connections to book stores. You are responsible for building your own audience. It also makes no claim on ownership nor distribution rights of your work. Do not bank on being paid (which is again 99% accurate).
Yes, Tapas does sort of promote some titles by listing them on the front page of the app. Yes, Tapas does offer tiny payments in the forms of ad revenue sharing.
Are there enough readers to be worth it? I dunno. Only you know what is an adequate audience to you. Some analysis has been done previously to look at what size readership to expect, but the samples provided were so few and diverse that mathematical analysis would have been meaningless. Some creators throw crying fits when a new series doesn't grow beyond the four digit subscriber mark within the first month, and other creators dance in the streets if their book gets double digit subscribers after a year.
From time to time, some genres or trends will fair better than others due to popularity. You may see mentions in the forum about the popularity of BL which has been the most popular category for a few years now. Horror and Romance are also strong contenders across both comics and novels. All genres are welcome, and last year a Western of all things did very well and became a premium title.
Tapas does have a few features which give it a leg up compared to -- say -- Watpad. These features include this community forum (Webtoons doesn't even have one), optional audio through a plugin utilizing Soundcloud, access to a comment section on each episode (limited to website users), creator pages for blogging, series hashtags for searching (the episode hashtags don't actually do anything), emojis, and integration of pictures. That last feature requires using a workaround technique called the Firefox Method, but it's a functional feature.