Hi John,
To add an image, this article might help you: https://medium.com/tantalizing-tales/adding-an-image-to-your-draft-story-24d3615fc1a
And this is also a great publication to get eyes on your erotica, with high engagement from the editors.
As for the tip feature, if you click on your profile pic, then Settings and click the tab 'Publishing', you can turn it on there.
Setting up a paywall is the same as the Medium Partnership Program and you can only apply for that when you have 100 followers. Best things is to get your work out there, as that will get you followers.
Hope this helps!