Hi!
If you have both eeschema and pcbnew open, clicking a symbol in the schematic should highlight a footprint in the PCB and vice-versa. It also works for nets - tracks.
It’s not possible. There’s a wishlist item for that for v6 which will likely be implemented, but it won’t help you soon.
If you use hierarchical sheets you can select a footprint in the board editor, open context menu->Select and select all footprints from the same hierarchical sheet.