I've commented on the parallax in other threads, so I'll just say it's customizable in game to do what you want. Do check out the current available mod settings.
Camera dragging with the mouse is a known limitation noted on the mod page; It's affected other kinds of mods too and I believe there is an API request to allow updating character positions during dragging.
I experimented with fade in quite a bit before settling on having the planet scale up instead. There wasn't a nice way to slowly fade in the planet without creating a very large sprite sheet, at least as far as I was able to see. I'm not sure I fully understand how your gradient idea would work, as surely a white gradient on top of the planet would look pretty bad?
And lastly, as it's not currently possible to read the distance to a platform's destination, I can't start the planet animation until the platform actually arrives at the destination planet. I'd love to render the planet larger as the platform gets closer, but it's not possible in the current API. Again, there's an API request exists for this functionality so I'll be able to mess with this if it gets added in the future.