Yes, you can theoretically do code-only projects on mac and linux, but win is definitely the most comfortable dev platform for Stride.
Yea, some kind of converter for unity assets would be cool. But 3d assets should already work... And with other things from the Unity asset store you could run into licensing issue. But I don't know the details about that, might even vary from asset to asset.
As far as I can tell, as long as you pay for a unity asset and you don't just resell it by itself, you can use it in whatever way you want.
For example, if there's a nifty networking library for Unity and I adapted to use it somewhere else, as long as I don't resell the library, I should be fine. Practically I can't imagine an asset store author suing you for using the asset in a non-unity project.
I do vastly prefer a single language engine like Stride, versus Godot which supports visual scripting, GD script, and C#.
Plus you need to use a PC to develop.
Now I'm thinking Unity assets could be adapted to work with Stride since both use C#. If so, switching from Unity to Stride won't be so bad.