1. Row selection: It is not recommended to work with visual elements in a virtualized control (no matter if it is RadGridView, DataGrid, etc.). The thing is that each element is recycled and reused on scrolling.
What you should do in this case is to work with SelectedItems collection of the grid.
2. Multithreading: We do not provide such in RadGridView. I'm afraid that it's up to you to implement your business logic in such a way that it executes on a separate thread, but fires all the necessary notifications on the UI thread.
the Telerik team