Depends what your goal is really.
Approach 1: "Fail Faster"
Basically just publish your first draft online, don't set your expectations for building an audience too high, but rather consider this a training or data-gathering exercise. Assume that you will likely make mistakes, and then use the fact that it's widely available to get feedback from people and see what works and doesn't in real time.
After all, you can always take it down later and publish the second draft either on Tapas, or on other platforms or in print after working out the kinks.
Approach 2: "Make a Splash"
OR you can hold off, wait until you've been through your beta readers, written a second draft, have a decent number of chapters queued up, make or commission a really slick cover and banner, maybe some promo assets, and then start publishing when everything is ready to try to make the biggest impact possible. This way is better if your aim is building an audience, but it's definitely slower, more work up front, easy to get demotivated, so less good for building experience.