The tapas TOS literally allows for you to draw sex scenes as long as you censor the penetration, and the story itself is not porn (i.e. exists for titilation). I think you're worrying for nothing. The staff is also great about working with creators if they cross the line by mistake.
I'm less familiar with the rules on violence, but I've read some pretty messed up stuff and you're very likely fine there too.
But if you want clarification on any specific parts of the TOS, feel free to ask. It is sometimes vague on purpose to allow creators some freedom/grey area. It's not meant to be black and white, which is good for artistic work.
SIDENOTE the mature ban is specific to iOS, and comes from Apple, not Tapas. You're good on the desktop, but many of us no longer appear on the app. This is true of webtoon/similar sites too. It's cause Apple sucks.