 Here is the Python code based on your instructions, using the Kivy library:

```python
from kivy.uix.behaviors import FocusBehavior, CompoundSelectionBehavior
from kivy.uix.gridlayout import GridLayout
from kivy.core.window import Window
from kivy.uix.label import Label
from kivy.uix.button import Button

class SelectableGrid(FocusBehavior, CompoundSelectionBehavior, GridLayout):
    def __init__(self, **kwargs):
        super(SelectableGrid, self).__init__(**kwargs)
        self.selected_nodes = set()
        self.bind(selection_add=self.on_selection_add, selection_remove=self.on_selection_remove)

    def on_selection_add(self, instance, nodes):
        for node in nodes:
            node.background_color = (1, 1, 1, 1)  # RGBA for white
        self.print_selected_nodes()

    def on_selection_remove(self, instance, nodes):
        for node in nodes:
            node.background_color = (1, 1, 1, 0)  # RGBA for transparent
        self.print_selected_nodes()

    def print_selected_nodes(self):
        print("Selected nodes:", self.selected_nodes)

    def handle_key_down(self, instance, key):
        if key in [27, 'up', 'down', 'left', 'right']:  # Escape, up, down, left, right keys
            direction = {'up': -1, 'down': 1, 'left': -1, 'right': 1}[key]
            self.navigate_key(direction)
        elif key in [49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 48, 97, 98, 99, 100, 101, 102]:  # 1-9, 0, a-d
            self.select_with_key_down(getattr(Window, key))

    def handle_key_up(self, instance, key):
        if key in [27, 'up', 'down', 'left', 'right']:
            self.select_with_key_up(getattr(Window, key))

    def navigate_to_node_by_number(self, number):
        for child in self.children:
            if isinstance(child, Button) and int(child.text) == number:
                self.focus = child

    def handle_touch_down(self, touch):
        with self.touch_down(touch):
            self.collide_point(*touch.pos)
            if self.collide_point(*touch.pos):
                self.select_with_touch(touch.get_widget_at_pos(*touch.pos))

    def create_buttons(self):
        for i in range(1, 41):
            button = Button(text=str(i), size_hint=(1, 1 / 5))
            button.bind(touch_down=self.handle_touch_down)
            self.add_widget(button)

my_grid = SelectableGrid(cols=8, rows=5)
my_grid.create_buttons()

from kivy.app import App

class MyApp(App):
    def build(self):
        return my_grid

if __name__ == "__main__":
    MyApp().run()
```

This code creates a custom class named "SelectableGrid" that inherits from "FocusBehavior", "CompoundSelectionBehavior", and "GridLayout". It handles key down and key up events, navigates to a node by typing its number, selects and deselects nodes, and handles touch events. The selection of a node changes its background color, and the selected nodes are printed when the selection changes. The code also creates an instance of the class, adds 40 buttons to it, and binds the touch down event of each button to the touch handling method of the grid. Finally, it runs the application with the grid as the root widget.