Creators should have absolute choice in regards to all of those things.
I'm not sure how making speculations is making "conclusions". Two completely different things. I just think it is important for creators to know exactly what they are getting into before they get into it. In this case, from what it sounds like, you will be making the story and the art, but at the end of the day, Tapas will make the decisions about what happens to your story and art.
Look at it this way... say you make your comic and then Tapas decides to make a deal with a publisher that you don't like. For me, that would be Viz. So say Tapas decides to publish my comic with Viz, but then Viz sees that there's a panel of my comic that doesn't adhere to PG-13 standards. Instead of changing the rating, Viz instead asks Tapas if they can censor the panel. Tapas has the full right to say okay on that even though I am someone who personally is against censorship of any sort and would never allow that to happen to my comic.
Again, SPECULATION. Theoretically COULD/MIGHT happen. But creators should be aware when they sign a contract that this situation could be considered okay within the contract and if they don't want it to happen, then they should negotiate the contract or walk out on the deal.
This exact situation happened with the creators of Cyanide and Happiness. They actually walked out on a TV show deal because they couldn't negotiate the contract and were not given enough control over their content.