It's not streets that smell, it's the cars. And you're right - nobody enjoys having a walk near a street with heavy car traffic. That's why in Europe a lot of streets in the city centers are designed in a way to discourage driving, providing ring roads and public transport options instead.
No need to guess: https://liberapay.com/Liberapay/income/ . Most money goes to the creator of Liberapay, and I would not be surprised if it would mainly cover the costs of running the service.
I'm pretty sure that this (and a little bit more) is already present in KDE and it's called Activities. It's not very popular, possibly because it's not "marketed" enough IMO.
For what it's worth, Ripcord[1] can do that (okay, it can open channels in separate tabs that can be moved to separate windows). And it is a native (Qt) application.
The only problem is that it's not free (with unlimited trial, though) and the development seems to have stopped. Still works okay for text chat, though.
Hard to say if it'll be as smooth as iPhone, but my experience with PinePhone shows that Qt-based environments (Ubuntu Touch, SailfishOS, even KDE) are way smoother than Phosh, which is based on Gtk. PinePhone isn't the most powerful phone out there, but I'd risk saying that SailfishOS is pretty smooth on it.
Doesn't matter. The whole point of Delta Chat is that the other parties in the chat don't have to use it or even know about its existence. You lose encryption, but at least you can message those people. It looks just like any other email message.
With Flatpak you can have your own repositories. Therefore packages can be released as soon as developer wants, without depending on someone else deciding whether to allow for that or not.