Several of these will be addressed in the next (v1.7) release version.
- Added File -> New Card as a convenience.
- Fixed the undesirable interaction between Nav Gestures and canvas dragging; this was an oversight.
- Switching tools from the keyboard is a bit tricky; they need to be shortcuts that "cut across" a number of complex contexts to be really useful. I don't see any reasonable way to do this within the constraints of a web browser, but I've added mappings to F1-F12 for tool swapping in native-Decker, which addresses your use-case.
Double-click speed is really fiddly; as far as I know, SDL doesn't expose the OS-level double-click delay. If you do some experiments modifying DOUBLE_CLICK_DELAY in the source (which is measured in frames, at 60hz) I'll consider tweaking the value. Alternatively, you could use enter or space as a properties shortcut.