I plan to publish my app to the app store. The first version is pretty basic, and I plan to add more features. Would I be able to update the listing, after it would be accepted? (adding screenshots, modifying the description, change pricing, change staff pick banner)
I would like to know that as well!
Have you been able to do any updates (features, pictures, pricing) so far?
No, there won't, the review process is an one time thing. Once your app is accepted into the store there won't be any other reviews.
Please keep in mind that this is as of now, I don't know whether they will change this policy in the future.
Yes, as long as it meets the listing requirements. Check this out: https://shopify.dev/apps/store/success/prohibited-actions