as far as i know the only time you'll have to email Tapas submissions is if your looking to become premium/ a tapas exclusive but in terms of general publishing on the site there's no requirements. The only requirements in place are those laid out in the terms of service as far as minimum age for a user and for revenue programs.
I don't recall the word count limit but I'm sure there might be a few threads in the novel category of the forums that might give better details. I do know there's no limit on episodes (at least afaik) since there's comics with hundreds of episodes. The only limitations on themes are in regards to NSFW content, violence and the like, which again are laid out in the sites TOS
You can check out the site terms here:
and the content guidelines here:
there's a help page here:
https://help.tapas.io/hc/en-us
and this pinned forum thread that gives some useful tips and allows for some introduction the help get you settled: