Hi Rubens,
You're product sounds really exciting, I can't wait to see it. In terms of choosing a marketplace, we don't make you choose. Unlike certain marketplaces I could mention we do not penalize you if you do not list exclusively with us. We are the only official marketplace for Adobe CC extensibility and there is no cost in signing up or any fees. We don't share sales volume but you can see which are the most popular extensions on Exchange via the drop down filters. You mention "after effects templates", you may want to look at Adobe Stock, to see if it would be more suitable if you are essentially looking to sell content rather than some sort of extension which builds something in After Effects. Selling content is different and so is the total addressable market versus building some of panel/extension but the prices are also likely very different.
In terms of benefits and other questions, alt of it is covered in this FAQ: Exchange Documentation
As for the 90% revenue that goes to you, that's higher than any other comparable marketplace I can think of!
I hope that helps.
Jonathan